#include<cstdio>
#include<cstdlib>
#include<algorithm>
#include<cstring>
#include<cmath>

using namespace std;
int n, k, a[100];
int main(){
    scanf("%d%d", &n, &k);
    for (int i=0; i<n; i++)
        scanf("%d", &a[i]);
    int sum = 0;
    for (int i=0; i<n; i++)
        sum += a[i];
    int ans = 0;
    while (2*(sum+ans*k) < (ans+n)*(2*k-1))
        ans++;
    printf("%d\n", ans);
    return 0;
}

#include<cstdio>
const int maxn = 110;
int a[maxn];
int main() {
	int n, k;
	int m;
	scanf("%d%d", &n, &k);
	for (int i = 0;i < n;i++)
		scanf("%d", a + i);
	m = 2 * k*n - n;
	for (int i = 0;i < n;i++)
		m -= 2 * a[i];
	printf("%d\n", m > 0 ? m : 0);
	return 0;
}

#include <iostream>
#include <algorithm>
#include <string>
#include <cmath>
using namespace std;
int n, a[101], k, t = 0;
int main()
{
	cin >> n >> k;
	for(int i = 1; i <= n; i++){
		cin >> a[i];
		t += a[i];
	}
	for(int i = 0;; i++){
		if(i != 0)
			t += k;
		//cout << t << endl;
		if(i != 0)
			n++;
		double m =(double) t / n;
		//cout << "m=" << m << ' ' << int (m + 0.5) << endl;
		if(int(m + 0.5)== k){
			cout << i << endl;
			return 0;
		}
		//if(i == 10)
			//return 0;
	}
	return 0;
}

#include <iostream>

using namespace std;

int main()
{
    float n,i,m,s=0,j;
    float p=0,k;
    cin>>n>>k;
    for(i=0;i<n;i++)
    {
        cin>>m;
        s=s+m;
    }

    j=k*2*n-n-2*s;
    if(j>=0)
    {
      cout<<j;
    }
    else
    {
        cout<<"0";
    }

        return 0;
}

#include<bits/stdc++.h>
using namespace std;

int n,k,sum=0,cnt=0;

int main()
{

    cin>>n>>k;
    for(int i=1;i<=n;i++)
    {
        int x;
        cin>>x;
        sum+=x;
    }
    double tb=(double)sum/n;
    while( tb <(double)(k-0.5))
    {
        cnt++;
        sum+=k;
        tb=(double)sum/(n+cnt);
    }
    cout<<cnt;
}

#include <iostream>

using namespace std;

long long n, k, sum, x, mid, st, dr, N, Sum, i;

int main () {
    cin>>n>>k;
    for (i=1;i<=n;i++) {
        cin>>x;
        sum += x;
    }

    if (2 * sum >= n * (2*k-1)) {
        cout<<0;
        return 0;
    }
    st = 1;
    dr = 1000000000000LL;
    while (st <= dr) {
        int mid = (st + dr)/2;
        Sum = sum + mid * k;
        N = n + mid;

        if (2 * Sum >= N * (2*k-1))
            dr = mid-1;
        else
            st = mid+1;

    }
    cout<<st;
    return 0;
}

///MD.Himon Shekh

#include<bits/stdc++.h>
using namespace std;
//#define pi 2.0*acos(0.0)
#define nl '\0'
//#define sort(srt,n,grt)  sort(srt, srt+n, greater<int>());
//#define sort(srt,n) sort(srt,srt+n);
#define inf 1000000000
#define mem(a, b) memset(a, b, sizeof(a))
#define memc(arr,ar) memcpy(arr, ar, sizeof(arr))
#define all(x) (x).begin(), (x).end()///reverse(all(s));
typedef unsigned long long ull;
typedef long long ll;

//const int N = 1e7 + 7;
//bool used[N];

int main()
{
    double n,k,m,totm=0,ad,num;
    cin>>n>>k;
    for(int i=1;i<=n;i++){
        cin>>m;
        totm+=m;
    }
    double av=totm/n;
    int in=av;
    if(in==av){}
    else {
        double dis=av-in;
        if(dis>=0.5)in++;
    }
    av=in;
    if(av>=k){
        cout<<"0"<<endl;return 0;
    }
    ad=av+1;
    if(ad>=k)ad=k;
    num=n;
    double tot=totm;
    while(av!=k){
        totm+=ad;n++;
        av=totm/n;
        in=av;
        //cout<<in<<" "<<av<<" "<<ad<<endl;
        if(in==av){}
        else {
            double dd=av-in;
            if(dd>=.5){
                in++;
                av=in;
                if(av!=k){ad++;
                        if(ad>k)ad=k;
                        else{totm=tot;
                        n=num;}
                }
            }
        }
    }
    cout<<n-num<<endl;
return 0;
}

#include <bits/stdc++.h>
using namespace std;

int main(void){
	double k,a[900000], sum = 0;
	int n,i,p;
	scanf("%d %lf", &n, &k);

	for(i = 0; i < n; i++){
		scanf("%lf", &a[i]);
		sum += a[i];
	}
	if(sum / n >= (k-.5)){
	   	printf("0\n");
		return 0;
	}
	else{
		for(p = 1;;p++){
			sum += k;
			if((sum/(n+p)) >= (k-.5)){
				printf("%d\n", p);
				return 0;
			}
			else continue;
		}
	}

/*	double c = 0;
	if(sum / n >= k){
	   	printf("0\n");
		return 0;
	}
	else{
		for(i = 0,p = 0; ;i++,p++){
			if((sum+i*k)/(n+p) != (k-.5)) c++;
			else break;
		}
	}
	printf("%.0lf\n", c);
	*/
}

#define _CRT_SECURE_NO_WARNINGS
#include<iostream>
#include <bitset>
#include<algorithm>
#include<string>
#include<stdio.h>
#include<cmath>
#include<vector>
#include<queue>
#include<deque>
#include<stack>
#include<set>
using namespace std;

int main()
{
	ios_base::sync_with_stdio(0); cin.tie(NULL), cout.tie(NULL);
	int n, k,sum=0,a;
	cin >> n >> k;
	for (int i = 0; i < n; i++)
	{
		cin >> a;
		sum += a;
	}
	int av = sum / n;
	if ((av >= k) || ((sum%n) * 10)/n >= 5 && av == k - 1)
	{
		cout << 0 << endl;
		return 0;
	}
	else
	{
		int c = 0;
		while (1)
		{
			if ((av >= k) || (((sum%(n+c)) * 10)/(n+c)) >= 5 && (av == k - 1))
				break;
			c++;
			sum += k;
			av = sum / (n + c);
		}

		cout <<c<< endl;

	}
	return 0;
}

#include <cstdlib>
#include <iostream>
#include <string>
#include <string.h>
#include <math.h>
#include <map>
#include <vector>
#include <set>
#include <queue>
#include <algorithm>
#include <functional>
#include <iomanip>
#include <stdio.h>
#include <stdlib.h>
#include <memory.h>
#include <complex>
using namespace std;
typedef long long         ll;
ll modulo(ll m , ll n){
    return m >= 0 ? m%n : (n-abs(m%n))% n ;
}
int main() {
   ll n , k ,y;
    cin>>n>>k;
  float sum=0 ;
    for(int i =0 ; i <n ; i++){
        cin >> y;
        sum+=y;
    }
if( round ( sum/n ) +0.5 >= (k) ) {
            cout << 0 ;
            return 0;
        }
    for(int i =1 ; i <=100000000 ; i++){
        sum+=k ;

        if( ( round( sum/(n+i) ) +0.5)   >= k ) {
            cout<< i ;
            return 0;
        }
    }

}

#include <bits/stdc++.h>
using namespace std;

int main()
	{
	ios_base::sync_with_stdio(false);
	int n, k, i, sum=0,m;
	cin>>n>>k;
	int arr[n];
	for(i=0;i<n;i++)
		{
		cin>>arr[i];
		sum=sum+arr[i];
		}
	if(2*sum<n*(2*k-1))
		{
		m=n*(2*k-1)-2*sum;
		cout<<m<<endl;
		}
	else
		cout<<"0"<<endl;
	return 0;
	}

#include <bits/stdc++.h>
using namespace std;
int a[100000];
int main()
{
  int n,k,ans=0,x,sum=0;
  cin>>n>>k;
  bool f=0;
  for(int i=0; i<n; i++)
  {
    cin>>x;
    sum+=x;
  }
  while(1)
  {
    if(round(sum*1.0/(n+ans))==k)
    {
    	cout<<ans<<endl;
    	return 0;
	}
      sum+=k;
    ans++;
  }
  return 0;
}

# include<iostream>
using namespace std;
int n,k,l;
double s,j;
int mas[1000];
int main()
{
cin>>n>>k;
l=n;
for(int i=0; i<n; i++)
{
cin>>mas[i];
s=s+mas[i];
}
j=s/n+0.5;
int g=j;
if(g==k)
cout<<0<<endl;
else
{
while(true)
{
   l++;
   s=s+k;
  j=s/l+0.5;
  g=j;
   if(g==k)
   {
           cout<<l-n<<endl;
           break;
           }
           }
           }

           return 0;
           }

#include <iostream>
#include <algorithm>
#include <vector>
#include <deque>
#include <cassert>
#include <queue>
#include <stack>
#include <set>
#include <map>
#include <cstdio>
#include <string>
#include <utility>
#include <cmath>
#include <list>
#include <bitset>
#include <iomanip>
#include <functional>
using namespace std;
typedef long long ll;
typedef pair<int, int> ii;
typedef vector<ll> vi;
typedef long double ld;
typedef set<int>::iterator sit;
typedef map<int, int>::iterator mit;
typedef vector<int>::iterator vit;
#define fi first
#define se second
#define pb push_back
#define forn(i, n) for (int i = 1; i <= n; i++)
#define fore(i, n) for (int i = 0; i < n; i++)

vector<int> vt;

int main() {
	int n, k;
	cin >> n >> k;
	double s = k - 0.5;
	vt.resize(n);
	fore(i, n) {
		cin >> vt[i];
	}
	int cnt = 0;
	fore(i, n) {
		cnt += vt[i];
	}
	int r = 0;
	double i = 0;
	for (i = vt.size(); ; i++) {
		if (cnt / i > s)break;
		cnt += k;
		r++;
	}

	if(r)printf("%d\n", r - 1);
	else cout << 0;

	return 0;
}

/*#include<bits/stdc++.h>
using namespace std;
int i,j,k,l;
int main()
{
    double n,k;
    while(scanf("%lf%lf",&n,&k)!=EOF)
    {
        double sum=0;
        int ans=0;
        for(i=0;i<n;i++)
        {
            double temp;
            scanf("%lf",&temp);
            sum+=temp;
        }
        while(sum*1.0/n<(k-0.5))
        {
            sum+=k;
            n++;
            ans++;
        }
        printf("%d\n",ans);
    }
    return 0;
}*/
#include<cstdio>
#include<iostream>
#include<cstring>
#include<algorithm>
using namespace std;
const int N=1e6;
int main(){
    int a[100];
    int n,m;
    double sum,ave;
    while(~scanf("%d",&n)){
        scanf("%d",&m);
        sum=0;
        for(int i=0;i<n;i++){
            scanf("%d",&a[i]);
            sum+=a[i]*1.0;
        }
        ave=sum/n;
        if(ave>=(m*1.0-0.5)) printf("0\n");
        else{
            for(int i=1;i<=N;i++){    //�����NҪ��һЩ����һ��ʼд��i<=n*m,̫С�ˣ���wa(�i�s^�t�i)
                sum+=m*1.0;
                ave=sum/(n+i);
                if(ave>=(m*1.0-0.5)){
                    printf("%d\n",i);
                    break;
                }
            }
        }
    }
    return 0;
}

#include <iostream>
#include <math.h>
#include <algorithm>

using namespace std;

int main() {
	long long ans, k, n, now, sum = 0, x, unusable;
	cin >> n >> k;
	for (int i = 0; i < n; i ++) {
		cin >> now;
		sum += now;
	}
	ans = ceil(2 * (n * (k - 0.5) - sum));
	x = 0;
	cout << max(ans, x) << endl;
	return 0;
}

#include <iostream>
#include <math.h>
#include <algorithm>

using namespace std;

int main() {
	long long ans, k, n, now, sum = 0, x;
	cin >> n >> k;
	for (int i = 0; i < n; i ++) {
		cin >> now;
		sum += now;
	}
	ans = ceil(2 * (n * (k - 0.5) - sum));
	x = 0;
	cout << max(ans, x) << endl;
	return 0;
}

#include <bits/stdc++.h>
#define LL long long
using namespace std;
LL n, k, s = 0, x, a;
int main()
{
    scanf("%lld%lld", &n, &k);
    for(LL i = 0; i < n; i++)
	{
        scanf("%lld", &x);
        s += x;
    }
    a = (2 * k - 1) * n - 2 * s;
    if(a < 0)
		a = 0;
    printf("%lld", a);
    return 0;
}

#include <bits/stdc++.h>
using namespace std;

int main()
{
   int num,maxi;
   cin>>num>>maxi;
   int*arr=new int[num];
   float avg;
   float sum=0;
   for(int i=0;i<num;i++)
   {
       cin>>arr[i];
       sum+=arr[i];
   }

   avg=sum/num;
   int counter=num;
   int print=0;
   float sum1=0;
    while(true){

       if(avg<maxi-0.5)
       {
           counter++;
           sum+=maxi;

       avg=sum/counter;
       print++;
       }
       else if(avg>=maxi-0.5)
       {
           break;
       }
    }

   cout<<print<<endl;
}

#include<bits/stdc++.h>
using namespace std;
int rVAL(int a,int b)
{
    double c,d,avg;
    c=(double)a/(double)b-a/b;
    if(c<0.5)
        return a/b;
    else
        return a/b+1;

}

int main()
{
    int n,k,i,sum=0,avg=0;
    scanf("%d %d",&n,&k);
    double x=0,t=k-0.5;
    int a[n];
    for(i=0;i<n;i++)
    {
        scanf("%d",&a[i]);
        sum+=a[i];
    }
    avg=rVAL(sum,n);

    x=(t*(double)n-(double)sum)*2;
    if(x>0)
        printf("%0.0lf\n",x);
    else
    cout<<"0"<<endl;

}

#include<iostream>
#include<string.h>

using namespace std;
int main()
{

    int n,k;double sum=0;
    cin>>n>>k;
    double a[n];
    for(int i=0;i<n;i++)
    {  cin>>a[i];
        sum+=a[i];
    }
    int count=0;
    double rand=k-1.0;
    rand=rand+0.5;

    while(1)
    {
        if((sum/n)>=rand)
        {  cout<<count<<endl;
            break;}
        sum+=k;
        n++;
        count++;
    }

}

//author:satwik_bhv1
#include<bits/stdc++.h>
//datatypes
#define ll long long
#define ld long double
//loops
#define fr(i,z,n) for(ll i=z;i<n;i++)
#define br(i,z,n) for(ll i=z;i>n;i--)
//operations
#define mp  make_pair
#define ff  first
#define ss  second
#define pub push_back
//map
#define mi map<ll,ll>
//vectors
#define vi vector<ll>
#define vpi vector<pair<ll,ll> >
//constants
#define pi 3.1415926535897932384626
#define mod 998244353
/*notes
    Don't use inbuilt fun for power
    Range of longlong=(-9,223,372,036,854,775,808 to 9,223,372,036,854,775,807 )
    INT_MAX = 2147483647(aprox 2*10^10)
    INT_MIN = -2147483648
    LLONG_MAX = 9223372036854775807
    LLONG_MIN = -9223372036854775808
    MST -> kruskal(DSU)
    sssp -> Dijkstras
    apsp -> Floydwarshall
    __gcd is the function in built for hcf
*/
//start
using namespace std;
//functions
void fast() { ios_base::sync_with_stdio(false); cin.tie(NULL); cout.tie(NULL); }
bool sortbysec(const pair<ll, ll>& a, const pair<ll, ll>& b) { return (a.second < b.second); }
void solve()
{
    ll n,k;
    cin>>n>>k;
    ll sum=0;
    fr(i,0,n)
    {
        ll a;
        cin>>a;
        sum+=a;
    }
    ll cnt=0;
    while((ld)sum<(ld)(k-0.5)*(ld)n)
    {
        cnt++;
        n++;
        sum+=k;
    }
    cout<<cnt;
}
int main()
{
    fast();
    ll t;
    //cin>>t;
    t=1;
    while(t--)
    {
        solve();
    }
}

#include<bits/stdc++.h>
using namespace std;

#define Fast ios::sync_with_stdio(false);cin.tie(NULL);cout.tie(NULL);
#define int long long
#define ld long double
#define S second
#define F first
#define mp make_pair
#define ms(x,y) memset(x,y,sizeof(x))
#define pb push_back
#define sl(n) cin>>n
#define pl(n) cout<<n
#define sze(v) (int)(v.size())

typedef vector<int>Vl;
typedef pair<int,int>pii;
typedef vector<pii>Vll;
typedef vector<vector<int>>Vv;
typedef vector<pair<int,pii> >Vlll;
typedef priority_queue <int, vector<int>, greater<int>>PQL;
typedef unordered_map<int,int>ump;

const int mod=1e9+7;
const int modx=998244353;
const int Nx=1e5+2;
const int inf= (int)(1e19+10LL);
bool poss(Vl arr,int md,int k,int sum){
	int val=k*md;
	sum=sum+val;
	ld avg=(1.0*sum)/(sze(arr)+md);

	if((avg+0.5)>=k)return true;
	return false;
}

void solve(){
   int n,k;
   sl(n);sl(k);
   Vl arr(n);
   int sum=0;
   for(int i=0;i<n;i++){
	   sl(arr[i]);
	   sum+=arr[i];
   }
   int low=0,high=(sum/n)+100000,ans;

   while(low<high){
	   int md=(low+high)/2;
	   if(poss(arr,md,k,sum)){
		   ans=min(ans,md);
		   high=high-1;
	   }
	   else{
		   low=low+1;
	   }
   }
   cout<<ans<<endl;

}

signed main(){
   int test=1;
   //sl(test);
   while(test--){
      solve();

   }
  return 0;
}

#include<bits/stdc++.h>
using namespace std;
int main(){
	double x,i,j,n,k;
	long long c=0;
	vector<double>v;
	double d,sum=0;
	cin>>n>>k;
	for(i=0;i<n;i++){
		cin>>x;
		v.push_back(x);
		sum+=x;
	}
	while(1){

		d=sum/(n+c);
		if(d>=(k-0.5)){
			break;
		}
        sum+=k;
		c++;
	}
	cout<<c<<"\n";
}

#include<bits/stdc++.h>
using namespace std;
int main(){
	double x,i,j,n,k;
	long long c=0;
	vector<double>v;
	double d,sum=0;
	cin>>n>>k;
	for(i=0;i<n;i++){
		cin>>x;
		v.push_back(x);
		sum+=x;
	}
	while(1){

		d=sum/(n+c);
		if(d>=(k-0.5)){
			break;
		}
                sum+=k;
		c++;
	}
	cout<<c<<"\n";
}

#include<bits/stdc++.h>

using namespace std;

int main(){
    double n, k, a[111], sum = 0, ans = 0;
    cin >> n >> k;
    for(int i = 1; i <= n; i ++){
        cin >> a[i];
        sum += a[i];
    }while(sum / n <= k - 0.5){
        sum += k;
        n++;
        ans++;
    }
    cout << max(ans - 1, 0.0);
    return 0;
}

#include <iostream>
#include <cstdio>
#include <cmath>
#include <cstring>
#include <climits>
#include <cstdlib>
#include <algorithm>
#include <ctime>

using namespace std;

const int len = 100010;
int n;
double ave,a[len],k;

int main() {
 //freopen("test.in","r",stdin);
 cin >> n >> k;
 double sum=0;
  for (int i=1;i<=n;i++) {
   cin >> a[i];
   sum+=a[i];
  }
  if (sum/n>=k-0.5)
  cout << 0 << endl;
  else {
  int i=1;
   while (ave<k-0.5) {
    sum+=k;
    ave=sum/(i+n);
    i++;
   }
   cout << i-1 << endl;
  }
 return 0;
}

#include <bits/stdc++.h>

using namespace std;

int main()
{
    int n,k,i,sum=0,avg_int,result=0,num,c=0,p_int,r=0,l=0;
    float avg=0,sub,p,sub1;
    cin >> n >> k;
    num=n;
    int a[n];
    for(i=0;i<n;i++)
    {
        cin >> a[i];
        sum = sum+a[i];
    }
    avg_int = sum/n;
    avg = (float)sum/n;
    //printf("%f",avg);
    if(avg>=avg_int){
        sub = avg - avg_int;
    }
    else{
        sub = avg_int-avg;
    }

    if(sub>=0.5 && avg>=avg_int)
    {
        result = avg_int+1;
    }
    else if(sub>=0.0 && sub<=0.49 && avg>=avg_int)
    {
        result =avg_int;
    }

    if(result==k)
    {
       printf("0");
    }

    if(result<k)
    {
        while(sum!=0)
        {
            num++;
            c++;
            sum = sum+k;
            p =(float)sum/num;
            p_int = sum/num;
            if(p>=p_int)
            {
                sub1 = p-p_int;
            }
            else{
                sub1 = p_int-p;
            }

            if(sub1>=0.5 && p>=p_int)
            {
                r = p_int+1;
            }
            if((sub1<=0.49 && sub1>=0.1)&& (p>=p_int))
            {
                r = p_int;
            }

            if(r==k)
            {
                l=1;
                break;
            }

        }
    }
    if(l==1)
    {
       printf("%d",c);
    }
    return 0;
}

#include <bits/stdc++.h>

using namespace std;

float n,k,m;
int t;

int main()
{
    cin>>n>>k;
    for(int i=0;i<n;i++){
        cin>>t;
        m+=t;
    }
    t=0;
    while(round(m/(n+t))<k){
        m+=k;
        t++;
    }
    cout<<t;
    return 0;
}

#include <iostream>
#include <cmath>

using namespace std;

int main()
{
    int n, k, sum = 0;
    cin >> n >> k;
    for(int i = 0; i < n; ++i)
    {
        int x;
        cin >> x;
        sum += x;
    }
    int le = -1, ri = 1e7;
    while(ri - le > 1)
    {
        int m = (ri + le) / 2;
        double res = double(sum + m * k) / (n + m);
        int x = int(res + 0.5);
        if(x < k)
            le = m;
        else
            ri = m;
    }
    cout << ri << endl;
    return 0;
}

#include<bits/stdc++.h>
using namespace std;
#define ll long long
ll n,ans,k,res,temp1;
int main()
{
    cin>>n>>k;
    for(int i=0;i<n;i++)
    {
        cin>>temp1;
        ans+=temp1;
    }
    double temp=round(ans/((double)n));
    while(temp!=k)
    {
        ans+=k;
        n++;
        res++;
        temp=round(ans/((double)n));
    }
    cout<<res<<endl;
return 0;
}

#include <iostream>
using namespace std;
int main() {
	int n, m;
	cin >> n >> m;
	int a[505]; double mij = 0; int mij1 = 0; int u = 0;
	for (int i = 0; i < n; i++) {
				cin >> a[i];
	}
	for (int i = 0;; ++i) {

		if (i >= n) {
			double ans = mij; int y = mij1;
			ans /= n+u;
			y /= n + u; ++u;
			if (ans - 0.5 >= y) {
				y++;
			}
			if (y == m) {
				cout << u-1;
				return 0;
			}
			else {
				y = 0;
				mij1 += m;
				mij += m;
			}
		}
		else {
			mij += a[i]; mij1 += a[i];
		}

	}

}

#include <iostream>

using namespace std;

int main(){
int n,k;
cin>>n>>k;
int nf=0,mrk;
while(n){
    n--;
    cin>>mrk;

    nf+=2*(k-mrk)-1;
}
if(nf<0)cout<<0;
else cout<<nf;
}

#include<bits/stdc++.h>
#include<algorithm>
using namespace std;

typedef long long ll;
typedef unsigned long long ul;
typedef pair<int,int> p;

#define N 100010
#define pi pair<int,int>
#define pb push_back

#define test \
        int t; \
        scanf("%d",&t);\
        while(t--)
ll llmax = numeric_limits<long long>::max();
ll llmin= numeric_limits<long long>::min();

ll arr[N],ar[N],nat[N];
char off[110][110];
int testar[N];
//char arr[110][1010];
vector<int>v;
vector<pair<int,pair<int,int>>>pv;

map<ll,ll>mp;

//priority_queue<p, vector<p>, greater<p> > pq;
priority_queue<int,vector<int>,greater<int>>pq;
//priority_queue<pair<int,int>,vector<pair<int,int>>,greater<pair<int,int>>>pqr;
priority_queue<pair<int,int>>pqr;

stack<char>st;

bool prime(ll num)
{
    ll mid=sqrt(num);
    for(int i=2; i<=mid; i++)
    {
        if(num%i==0)
            return false;

    }
    return true;
}

int main()
{
  long double n,k,sum=0,avg=0;
  cin>>n>>k;
  for(int i=0;i<n;i++)
  {
      cin>>arr[i];
      sum+=arr[i];
  }

avg=-((k-0.5)*n-sum)/(k-k-0.5);
if(avg>0)
    cout<<avg;
else
    cout<<"0"<<endl;

}

#include<stdio.h>
#include<math.h>
int main()
{
	int n,k ,i;
    double avg,sum=0;
	scanf("%d %d",&n,&k);
	int c[n];
	for(i=0;i<n;i++)
		scanf("%d",&c[i]) ;
	for(i=0;i<n;i++)
	{
		sum=sum+c[i];
	}

	avg=sum/n;

	if(round(avg)==k)
		printf("0");
	else
	{
        for(i=1; ;)
		{
			sum=sum+k;

			if(round(sum/(n+i)) ==k)
			{printf("%d",i);
			break;

			}
			else
				i++;
		}

	}
}

#include<stdio.h>

int main()

{
    double n,k,sum,p;
    int i;
    scanf("%lf%lf",&n,&k);
    k=k-.5;
    sum=0;
    for(i=0;i<(int)n;i++){
        scanf("%lf",&p);
        sum=sum+((k-p)/.5);
    }
    if(sum<0){
        printf("0\n");
    }
    else{
        printf("%d\n",(int)sum);
    }
    return 0;
}

#include<bits/stdc++.h>
using namespace std;
int a,n,sum,k;
int main()
{
	cin>>n>>k;
	for(int i=0;i<n;i++)
	{
		cin>>a;
		sum+=a;
	}
	for(int i=0;;i++)
	{
		if(floor(1.0*(sum+i*k)/(n+i)+0.5)==k)
		{
			cout<<i<<endl;
			return 0;
		}
	}
}

/*
rohit645
Rohit Kumar
*/

#include <bits/stdc++.h>
using namespace std;

typedef long long ll;
typedef double ld;
typedef pair < ll, ll > pll;
typedef vector < vector < ll > > matrix;

#define pb push_back
#define debug(x) cout << (#x) << " is " << (x) << endl
#define fast_io() ios_base :: sync_with_stdio(0); cin.tie(0); cout.tie(0)

const ll mod = 1e9 + 7;
const ll inf = LLONG_MAX;
const ll N = 1e5 + 10;

int main (void) {
    fast_io();
    ll k;
    double n;
    cin >> n >> k;
    ll temp = n;
    ll arr[temp];
    ll sum = 0;
    for (ll i = 0; i < temp; i++) {
        cin >> arr[i];
        sum += arr[i];
    }
    double cur_avg = sum / n;
    // debug(cur_avg);
    if (round(cur_avg) >= k) {
        cout << "0\n";
    }
    else {
        ll cnt = 0;
        while (round(cur_avg) < k) {
            sum += k;
            ++n;
            cur_avg = sum /(n);
            // debug(n);
            // debug(cur_avg);
            // debug(sum);
            cnt++;
            // debug(cur_avg);
            // debug(sum);
            // debug(n);
            // debug(round(cur_avg));
            // if (n == 7) {
            //     return 0;
            // }

        }

        cout << cnt << "\n";
    }

    return 0;
}

#include <cmath>
#include <cstdlib>
#include <cstdio>
#include <climits>
#include <iostream>
#include <iomanip>
#include <sstream>
#include <cstring>
#include <string>
#include <algorithm>
#include <vector>
#include <list>
#include <queue>
#include <set>
#include <map>
#include <unordered_map>
#include <functional>
#include <bitset>
using namespace std;

int main() {
    int n, t;
    double k, k2, csum=0, ans=0.0;
    cin>>n>>k;
    k2=k-0.5;
    for (int i=0; i<n; ++i) {
        cin>>t;
        csum+=t;
    }
    if ((csum/n)>=k2) {
        cout<<0<<endl;
        return 0;
    }
    ans=((k2*n)-csum)/(k-k2);
    cout<<ans<<endl;
    return 0;
}

#include <cstdio>
#include <cstdlib>
#include <iostream>
#include <vector>
#include <list>
#include <algorithm>
#include <array>
#include <string.h>
#include <ctime>
#include <memory>
#include <typeinfo>
#include <cmath>
#include <math.h>
#include <initializer_list>

int main() {
    std::ios_base::sync_with_stdio(false);
    int n, ans = 0;
    double k, s = 0;
    std::cin >> n >> k;
    std::vector<int> v(n);
    for(int i = 0; i < n; i++){
        std::cin >> v[i];
        s += v[i];
    }
    if(s / n >= k - 0.5)
        std::cout << ans;
    else{
        while(true){
            s += k;
            n++;
            ans++;
            if(s / n >= k - 0.5){
                std::cout << ans;
                break;
            }
        }
    }
    return 0;
}

#include <bits/stdc++.h>

using namespace std;

typedef long long ll;
typedef unsigned long long ull;

void debug_out() { cerr << endl; }
template <typename Head, typename... Tail>
void debug_out(Head H, Tail... T) {
  cerr << ' ' << to_string(H);
  debug_out(T...);
}

#define debug(...) cerr << '[' << #__VA_ARGS__ << "]:", debug_out(__VA_ARGS__)

int f(double s, double n, double k) {
  return -ceil(2 * (s - n * (k - 0.5)));
}

int main() {
  ios_base::sync_with_stdio(false); cin.tie(NULL); cout.tie(NULL);
  int n, k;
  cin >> n >> k;
  vector<int> arr(n);
  double s = 0;
  for (int i = 0; i < n; ++i) {
    cin >> arr[i];
    s += arr[i];
  }
  if (s / n >= k - 0.5) {
    cout << 0 << '\n';
  } else {
    int ans = 1e9, num = 1e9;
    for (int i = k; i >= 1; --i) {
      if (f(s, n, k) > 0) {
	ans = f(s, n, k);
	num = i;
	break;
      }
    }
    for (int i = 0; i < ans; ++i) {
      s += num;
    }
    assert (ans > 0 && s / (n + ans) >= k - 0.5);
    cout << ans << '\n';
  }
  return 0;
}

/*
  -------------
  Prateek Celly
  DA-IICT
  -------------
*/
#include<bits/stdc++.h>
using namespace std;

typedef long long ll;
typedef unsigned long long ull;
typedef long double ld;

#define pb push_back
#define mp make_pair
#define f first
#define s second
#define MOD 1000000007

int main(){
  ios_base::sync_with_stdio(false);
  cin.tie(NULL);
  cout.tie(NULL);
  ll n,k,sum=0,j=1,x; cin>>n>>k;
  for(ll i=0;i<n;i++) {cin>>x; sum+=x;}
  float v=float(sum)/n;
  if(v<(floor(v)+ceil(v))/2) v=floor(v); else v=ceil(v);
  while(v<k){
    sum+=k;
    v=float(sum)/(n+j);
    if(v<(floor(v)+ceil(v))/2) v=floor(v); else v=ceil(v);
    j++;
  }
  cout<<j-1;
  return 0;
}

#include <bits/stdc++.h>
using namespace std;

int main()
{
    //   freopen("input.txt","r",stdin);
    // freopen("output.txt","w",stdout);
    long long n,k;
    cin>>n>>k;
    int a[n];
    long long s=0;
    for(int i=0;i<n;i++)
    {cin>>a[i];s+=a[i];}
    long long c=0;
    if((s%n>=(n+1)/2 && s/n>=k-1) || (s%n==0&& s/n==k))
    cout<<0;
    else
    {
    for(long long i=0;i<=10000000;i++)
    {
        s+=k;
        n++;
        c++;
        if((s%n>=(n+1)/2 && s/n>=k-1) || (s%n==0&& s/n==k))
        break;
    }
    cout<<c;
    }
}

#include<iostream>

using namespace std;

int main()
{
	int res[105];
	double sum=0,n=0, k=0;
	cin >> n >> k;
	double sub = n+1,ss=n;
	for (int i = 0; i < n; i++)
	{
		cin >> res[i];
		sum += res[i];
	}
	if (sum / n >= (k - 0.5))
	{
		cout << 0 << endl;
		return 0;
	}

	while(1)
	{
		if (((sum + k) / sub) >= (k - 0.5))
		{
			cout << sub - ss << endl;
			break;
		}
		else
		{
			sub++;
			sum += k;
		}
	}
	return 0;

}

#include <iostream>

using namespace std;

int main()
{
    int n, k;
    float sum = 0;
    int num;
    cin>>n>>k;
    for(int i = 0; i < n; i++) {
        cin>>num;
        sum += num;
    }
    if(sum / n <= k && sum / n >= k - 0.5) {
        cout<<"0";
    } else {
        cout<<((k * n * 2) - sum * 2 - n);
    }

    return 0;
}

#include<iostream>
#include<math.h>
#include<algorithm>
#include<string>
#include<map>
#include<vector>
#include<set>
using namespace std;
const long long MOD = 1000000007;
void main() {
	long long n, m, d, n1,s=0;

	vector<int> OT;
	string s1, s2;
	cin >> n >> m;
	n1 = n;
	while (n > 0) {
		n--;
		cin >> d;
		s = s + d;
	}
	cout <<max(long long(0), 2 * n1*m - n1 - 2 * s);
//system("pause");
}

#include <bits/stdc++.h>
using namespace std;

int main()
{
    int t,k;
    cin>>t>>k;

    int s = 0;

    for(int i = 0 ; i < t ; i++)
    {
        int x; cin>>x;
        s += x;
    }

    int x = (t*(2*k-1))-2*s;

    if (x <= 0)
        cout<<0;
    else
        cout<<x;
}

#include<bits/stdc++.h>
using namespace std;
int main()
{
    int n,k;
    cin >> n >> k;
    int b;
    int sum=0;
    int x;
    for(int i=0;i<n;i++)
    {
        cin >> b;
        sum=sum+b;
    }
   // cout << (double)((double)sum/(double)n) << " " << (double)(k-0.5);
       if((double)((double)sum/(double)n)>=(double)(k-0.5))
       {
           cout << 0 << endl;
           return 0;
       }

        x=(int)(((n*(k-0.50))-sum)/0.50);
        cout << x << endl;

    return 0;
}

#include <iostream>

using namespace std;

int notas[1000];

int main()
{
    int n,k,sum,coc; cin >> n >> k; sum = 0;
    long long w;
    double res;

    for (int i = 0; i < n; i++)
    {
        cin >> notas[i];
        sum += notas[i];
    }

    res = (sum%n);
    coc = sum/n;
    //cout << sum << " " << res << " " << coc << endl;
    if ((res >= n/2 && coc >= k-1)||(res == 0 && coc == k))
    {
        cout << 0;
    }
    else
    {
        w = 2*((k*n)-sum-(0.5*n));
        cout << w;
    }
}

#include<bits/stdc++.h>
using namespace std;
int summ(int n)
{
     int sum=0;
     while(n)
     {
          int m=n%10;
          sum+=m;
          n/=10;
     }
     return sum;
}
int main()
{        int n,k;
        double sum=0.0,c=0;
        cin>>n>>k;
        int a[n];
        for(int i=0;i<n;i++)
        {
             cin>>a[i];
             sum+=a[i];
        }
        double x=sum/n;
        if(x>=k-0.5)
        cout<<0;
        else
        {
             for(int i=1;i<100000;i++)
             {
                  sum=sum+k;
                  n++;
                  c++;
                  if(sum/n>=k-0.5)
                  break;
                  else
                  continue;
             }
             cout<<c;
        }

}

#include <bits/stdc++.h>
#include <stdio.h>
#include <stdlib.h>
#include <cstdio>
#define ll long long
#define ull unsigned long long
#define all(v) ((v).begin()), ((v).end())
#define sz(v)   ((int)((v).size()))
#define forr(c,x,n)  for(long long c=x;c<n;c++)
#define fo(c,n)  for(long long c=n-1;c>=0;c--)
using namespace std;
typedef vector<long long> vi;
typedef set<long long>se;
/*
///////////////////////////////////////////////

**    **           **    *    **    **   **
**   **      *     **  *      **    **   **
**  **     *   *   ***        **    *******
** **     *     *  **         **         **
***      *       * **         **         **
** **     *     *  **     *****          **
**  **     *   *   **    *    **    **   **
**   **      *     **    *    **     **  **
**    **           **     ******       ***

///////////////////////////////////////////////
*/
// start +(end-start)/2
// sum from 1 to n = (n*(n+1))/2
//A=65 // a=97  // num=48
//decimal to binary :: while(n!=0) {r=(n%2==0 ?"0":"1")+r; n/=2;}
//int value = atoi(myString.c_str());
ll gcd(ll a,ll b){
    if(b==0)return a;
    else {
        return gcd(b,a%b);
    }

}
ll lcm(ll a,ll b){
return (a*b)/gcd(a,b);
}
ll revers(ll n){
int ans=0;
while(n){
    ans+=n%10;
    ans*=10;
    n/=10;
}
return ans/10;
}
string revers(string x){
char temp;
ll y=x.length();
forr(c,0,y/2){
temp = x[c];
x[c]=x[y-1-c];
x[y-1-c]=temp;
}
return  x;
}
bool prime(ll n )
{
    if(n==0||n==1)return 0;
    else if(n==2)return 1;
    else
    {
        for(ll c=2;c*c<=n;c++){
            if(n%c==0)return 0;
        }
        return 1;
    }
}
ll fac(ll n){
ll y =sqrt(n),ans=0;
for(ll c=1;c<=y;c++){
    if(n%c==0)ans++;
    if(n/c>y&&n%c==0)ans++;
}
return ans;
}
int numdig (ll n){
int ans=0;
while(n){
    n/=10;ans++;
}
return ans;
}
bool check(string x){
int ans=0;
forr(c,0,x.length())
{
    if(x[c]=='4')ans++;
    else if(x[c]=='7')ans--;
    else return 0 ;
}
if(ans==0)return 1;
else return 0;
}
vi fact; ll divi=2;
void factor(ll num){
if(num==1)return ;
divi=2;
while(num%divi!=0)divi++;
fact.push_back(divi);
factor(num/divi);
}
ll lowsearch(vi arr,ll k){
ll s=0,mid,en=arr.size()-1;
while(s<=en){
    mid=(s+en)/2;
    if(k<=arr[mid])en=mid-1;
    else if(k>arr[mid])s=mid+1;
}
if(en>=0)
return arr[en];
else
    return -1;
}
ll hisearch(vi arr,ll k){
ll s=0,mid,en=arr.size()-1;
while(s<=en){
    mid=(s+en)/2;
    if(k<arr[mid])en=mid-1;
    else if(k>=arr[mid])s=mid+1;
}
if(s<=arr.size()-1)
return arr[s];
else
    return -1;
}
int main()
{
 ios::sync_with_stdio(0);cin.tie(0);cout.tie(0);
 int n,k,ans=0,x,num=0;
 cin>>n>>k;
 num=n;double sum1,sum=0;
 forr(c,0,n){cin>>x;sum+=x;}
 while(sum1<1000000){
        sum1=sum/num;
    if(sum1==k||(k-sum1)<=.5){cout<<ans<<endl;break;}
    ans++;
    num++;
    sum+=k;
 }

return 0;
}

#include<bits/stdc++.h>
using namespace std;
typedef long long ll;
ll n,k,x,sum,da;
int main(){
	scanf("%lld%lld",&n,&k);
	for (int i=1;i<=n;i++){
		scanf("%lld",&x); sum+=x;
	}
	while (k!=round((sum+k*da)/1.0/(n+da))) da++;
	printf("%d",da);
    return 0;
}

#include <iostream>
#include <cstdio>
#include <cstdlib>
#include <algorithm>
#include <cstring>
double a,s=0.0;
int main()
{
	int n,k;int nn;
	scanf("%d%d",&n,&k);nn=n;
	for(int i=1;i<=n;i++)
	{
		scanf("%lf",&a);
		s+=a;
	}
	double t=s/n;
	int tt=(int)(t+0.5);
	while(tt!=k)
	{
		n++;
		s+=k;
		t=s/n;
		tt=(int)(t+0.5);
	}
	printf("%d",n-nn);
	return 0;
}

# include <bits/stdc++.h>
using namespace std;

int main()
{
    int n,k,aver,c,count;
    float z,sum,d;
    cin>>n>>k;
    double a[n];
    sum=0;
    for(int i=0;i<n;i++)
    {
        cin>>a[i];
        sum=sum+a[i];
    }
    z=n;
    aver=round(sum/z);
    count=0;
    c=aver;
    for(int l=1;c<k;l++)
    {
        sum=sum+k;
        d=n+l;
        c=round(sum/d);
        count++;
    }
    cout<<count<<endl;
    return 0;
}

#include<iostream>
#include<cstdio>
#include<cmath>
#include<string>
using namespace std;
int main(){
	int n,k,a[100001],sum=0,ans=0;
	cin>>n>>k;
	for(int i=1;i<=n;i++){
	cin>>a[i];
	sum+=a[i];
	}
	ans=max(0,2*n*k-n-sum*2);
	cout<<ans;
	return 0;
}

#include<bits/stdc++.h>
using namespace std;
int n,k,sum=0,x,a;
int main()
{
    cin>>n>>k;
    for(int i=1;i<=n;i++)
	{
    	cin>>x;
    	sum+=x;
	}
	a=(2*k-1)*n-2*sum;
    if(a<0)
	{
		a=0;
	}
    cout<<a;
    return 0;
}

#include<stdio.h>
int main() {
	int n, k, a[100];
	float s = 0, x = 0;
	scanf("%d %d", &n, &k);
	for (int i = 0; i < n; i++) {
		scanf("%d", &a[i]);
		s += a[i];
	}
	while (s / n < k - 0.5) {
		s += k;
		x++;
		n++;
	}
	printf("%.0f", x);
	return 0;
}

#include<stdio.h>
int n,k,a,sum;
main()
{
	scanf("%d%d",&n,&k);for(register int i=n;i--;){scanf("%d",&a);sum+=a;}
	for(register int i=0;;++i)
		if((int)((sum+k*i)*1./(n+i)+0.5)==k){printf("%d",i);return 0;}
}/**/

#include <iostream>
using namespace std;
int n,i,p,sum,ans;
double m,k;
int a[101];
int main ()
{
	cin>>n>>k;
for (i=1; i<=n; i++)
{
cin>>a[i];
sum+=a[i];
}

if ((1.0*sum/n+0.5)>=k) {cout<<0<<endl; return 0;}
p=n+1;
while (true)
{
sum+=k;
m=1.0*sum/p;
if ((m+0.5)>=k) {ans=p-n; break;}
else
p++;
}
cout<<ans<<endl;
return 0;
}

#include<bits/stdc++.h>
using namespace std;
int main()
{
    double ave;
    int k,n,total=0,res;
    int a[101];
    cin>>n>>k;
    res=n;
    for(int i=1;i<=n;i++)
    {
        cin>>a[i];
        total+=a[i];
    }
    ave=double(total)/double(n);
    while(ave<k-0.5)
    {
        res++;
        total+=k;
        ave=double(total)/double(res);
    }
    cout<<res-n<<endl;;
    return 0;
}

#include <bits/stdc++.h>
#include <vector>
#include <set>
#include <map>
#include <unordered_map>
#define lli long long int
#define loop(i,x,n) for(int i=x;i<n;i++)
#define loopr(i,x,n) for(int i=n-1;i>=x;i--)
#define st set<lli>
#define v vector<lli>
#define um unordered_map<lli,lli>
#define vpl vector<pair<lli,lli>>
#define llu long long unsigned
#define ms muliset<int,greater<int>>
#define ums unordered_map<string,lli>
#define pb push_back
#define time ios_base::sync_with_stdio(false); cin.tie(NULL); cout.tie(NULL);
#define test lli t; cin>>t; while(t--)
using namespace std;
int gcd(int a,int b)
{
    if(b==0) return a;
    return gcd(b,a%b);
}
v adj[100001];
lli vist[10001];

void dfs(lli node)
{
    vist[node]=1;
    for(lli child : adj[node]) if(!vist[child]) dfs(child);
}

int main()
{
    time
    lli n;
    cin>>n;
    double b;
    cin>>b;
    double b1=b-0.50;
    double avg=0;
    loop(i,0,n) { double d; cin>>d; avg+=d;}
    double avg1 = avg/n;
    lli c=0;
    while(avg1<b1)
    {
        n++;
        c++;
        avg+=b;
        avg1 = avg/n;
    }
    cout<<c<<endl;
    return 0;
}

#include<bits/stdc++.h>
using namespace std;

//var
int n,k,a,su = 0,us = 0;

int main(){
	cin >> n >> k;
	for(int i = 1; i<=n; i++){
		cin >> a;
		su += (k-a);
	}
	cout << max(0,2*su - n) << endl;
}

#include<bits/stdc++.h>

typedef long long ll;

using namespace std;
const ll INF = 10e17+7;

int main() {
   int n,k,m,sum=0,c=0;
   cin>>n>>k;
   for(int i=0;i<n;i++)
   {
       cin>>m;
       sum+=m;
   }
   double q=double(k)-0.5;
   //cout<<q;

   while(1)
   {
        if(sum+k*c>=q*(n+c))
            return cout<<c,0;
        c++;
   }
   //cout<<"0";

}

#include <iostream>
using namespace std;

 int main()
 {
 	int n,k,s=0,t,c=0;
 	cin>>n>>k;
 	while(n){cin>>t;s+=t;--n;++c;}
 	t=(2*k-1)*c-s*2;
 	if (t>0) cout<<t;
 	else cout<<0;
 }

# include <bits/stdc++.h>

using namespace std;

const int N = (int)157;

int n, k;

int a[N];

long double avg;

int main(){
  cin >> n >> k;
  for(int i = 1; i <= n; i++){
    int x;
    cin >> x;
    avg += x;
  }
  if(int(avg / n + 0.5) == k){
    cout << 0;
    return 0;
  }
  for(int i = 1; i <= 500000; i++){
    avg += k;
    if(int(avg / (n + i) + 0.5) == k){
      cout << i;
      return 0;
    }
  }
}

# include <bits/stdc++.h>

using namespace std;

const int N = (int)157;

int n, k;

int a[N];

long double avg;

int main(){
  cin >> n >> k;
  for(int i = 1; i <= n; i++){
    int x;

    cin >> x;
    avg += x;
  }
  if(int(avg / n + 0.5) == k){
    cout << 0;
    return 0;
  }
  for(int i = 1; i <= 500000; i++){
    avg += k;
    if(int(avg / (n + i) + 0.5) == k){
      cout << i;
      return 0;
    }
  }
}

#include <iostream>
using namespace std;

int n,k,sum,ans;
int a[110];

int main()
{
	cin>>n>>k;
	for(int i=1;i<=n;++i) cin>>a[i],sum+=a[i];
	while(1)
	{
		if((int)(sum*1.0/n+0.5)==k) break;
		sum+=k; n++; ans++;
	}
	cout<<ans<<endl;
	return 0;
}

#include <bits/stdc++.h>
#define mp make_pair
using namespace std;
typedef pair<int, int> pii;

int n, k, m;
long long ans, tmp;
int main() {
	ios::sync_with_stdio(false), cin.tie(0), cout.tie(0);
	cin>> n >> k;
	ans = 0;
	m = 0;
	for(int i = 0; i < n; i++) {
		cin>> tmp;
		ans += tmp;
	}
	int l = 0; int r = 300000;
	while(l <= r) {
		m = (l + r)/2;
		double tt = (double)(ans + m*k)/(n + m);
		if(tt < k - 0.5)
			l = m + 1;
		else
			r = m - 1;
	}
	if((double)(ans + m*k)/(n + m) < (k - 0.5)) m++;
	//if((double)(ans + (m - 1)*k)/(n + m - 1) > (k - 0.5)) m--;
	cout<< m << endl;
	return 0;
}

#include<bits/stdc++.h>
using namespace std;
int main()
{int n,m;
 cin>>n>>m;
 double sum=0;
 int x;
 for (int i=1;i<=n;i++){cin>>x;sum+=x;}
 int z=m;
 for (int i=0;;i++)
   {if(floor(sum/(n+i)+0.5)==m) {cout<<i;return 0;}
    sum+=z;}
}

#include<iostream>

using namespace std ;

#include<iostream>

using namespace std ;

int main()
{
int n;
float k;
cin>>n>>k;
float a[n];
int sum=0;
for(int i=0;i<n;i++){
	cin>>a[i];
	sum+=a[i];
}

if(sum/float(n)>=(k-0.5))
{
	cout<<0;
}
else{
cout<<2*k*n - 2*sum - n;
}
return 0;
}

#include <iostream>
#include <cstdio>
#include <cstring>
#include <algorithm>
#include <cmath>
#include <string>
#include <cstring>
#define INF 0x3f3f3f3f
#define ms(x,y) memset(x,y,sizeof(x))
using namespace std;

typedef long long ll;

const double pi = acos(-1);
const double eps = 1e-8;
const int maxn = 210;

int main()
{
	int n, k;
	cin >> n >> k;
		double sum = 0;
		for (int i = 0; i < n; i++)
		{
			int p;
			cin >> p;
			sum += p;
		}
		int i = 0;
		if ((int)(sum / n+0.5) >= k)
		{
			cout << 0;
			return 0;
		}
		for (i = 1;; i++)
		{
			int p = (sum + i*k) / (double)(n + i) + 0.5;
			if (p == k) break;
		}
		cout << i;
}

#include<bits/stdc++.h>
using namespace std;
typedef long long LL;
LL N,K;
LL sum=0;
LL toint(double aa) {
  return floor(aa+0.5);
}
LL solve() {

  cin>>N>>K;
  for(LL i=1;i<=N;i++) {
    LL xx;scanf("%I64d",&xx);
    sum+=xx;
  }

  double x=2*N*(K-0.5)-2*sum;

  return max(0LL,(LL)ceil(x));
}
int main() {
  printf("%I64d\n",solve());
  return 0;
}

#include<iostream>
#include<algorithm>
#include<stdio.h>
#include<cstring>
#include<cmath>
#include<map>
using namespace std;
long long func1(int n);
long long func2(int A,int B);
long long com[160000],a[300008];
int main()
{

    int n,m;
    while(cin>>n>>m!=NULL)
    {
        int N=n,sum=0,ans=0;
        double fin=m-0.5;
        while(N--)
        {
            int t=0;
            cin>>t;
            sum+=t;
        }
        if(sum/(n*1.0)>=fin)
        {
            cout<<ans<<endl;
            continue;
        }
        while(1)
        {
            sum+=m;
            n++;
            ans++;
            if(sum/(n*1.0)>=fin)
            {
                cout<<ans<<endl;
                break;
            }
        }
    }
    return 0;
}

#include<iostream>
using namespace std;
int main()
{ int i,a,sum=0,t, j;
   float n, m;
   cin>>n>>m;
   for(i=0; i<n;i++)
   { cin>>a;
     sum+=a;
   }
     if((sum/n)>=(m-0.5))
     {
       cout<<0<<endl;
     }
     else
     {
    j=(sum-((m-0.5)*n))/((m-0.5)-m);
    if(j<0)
    {j=-j;
    }
    cout<<j<<endl;
    }
return 0;
}

#include<cstdio>
#include<iostream>
#define LD long double
#define LL unsigned long long
using namespace std;
int main(){
	LD n,k;
	LD ans = 0,l,val;
	LL t = 0;
	cin >> n >> k;
	for(int i = 0;i < n;i++){
		cin >> l;
		ans += l;
	}
	for(int i = 0;i <= 10000000;i++){
		if((ans + i * k) / (i + n) >= (k - 0.500000)){
			val = i;
			break;
		}
	}
	cout << val << endl;
	return 0;
}

#include <iostream>
#include <cstdio>
#include <cstring>
#include <cstdlib>
#include <cmath>
#include <algorithm>
#include <string>
#include <vector>
#include <stack>
#include <bitset>
#include <set>
#include <list>
#include <deque>
#include <map>
#include <queue>
#define MOD 1000000007
using namespace std;
typedef long long ll;
const double pi=acos(-1.0);
const double eps=1e-6;
const int INF=1000000000;
const int maxn=100010;
const int maxm=10010;

int n,k,tmp,ans=0;
double sum=0.0;

int main()
{
	scanf("%d %d", &n, &k);
	for(int i=0;i<n;++i)
	{
		scanf("%d", &tmp);
		sum+=tmp;
	}
	ans=ceil(2.0*n*k-n-2.0*sum);
	ans=max(0,ans);
	printf("%d\n", ans);
    return 0;
}

#include<bits/stdc++.h>
#include <ext/pb_ds/assoc_container.hpp>
#include <ext/pb_ds/tree_policy.hpp>

#define ll long long int
#define ld long double
#define F first
#define S second
#define pb push_back

using namespace std;
using namespace __gnu_pbds;

typedef tree<ll, null_type, less<ll>, rb_tree_tag,
tree_order_statistics_node_update>
new_data_set;

const ll N=100005;

int main()
{
    ios_base:: sync_with_stdio(false);
    cin.tie(NULL); cout.tie(NULL);
    #ifndef ONLINE_JUDGE
    freopen("input.txt", "r", stdin);
    freopen("output.txt", "w", stdout);
    #endif
    // ll t;
    // cin>>t;
    // while(t--)
    {
        ll i,j,k,n,m,ans=0,cnt=0,sum=0;
        cin>>n>>k;
        ll a[n];
        for(i=0;i<n;i++){
            cin>>a[i];
            sum+=a[i];
        }
        ll lf=-1,rt=1e15;
        while(lf+1<rt){
            ll mid=(lf+rt)/2;
            ld ansd=(ld)(sum+(mid*k))/(ld)(n+mid);
            if((ll)(ansd+0.5)>=k){
                rt=mid;
            }
            else{
                lf=mid;
            }
        }
        cout<<rt;
    }
}

#include<bits/stdc++.h>
//#define int long long int
#define TRY_HARD ios_base::sync_with_stdio(false);  cin.tie(NULL);  cout.tie(NULL);
using namespace std;

//TRY_HARD TRY_HARD TRY_HARD TRY_HARD TRY_HARD TRY_HARD TRY_HARD TRY_HARD TRY_HARD TRY_HARD TRY_HARD TRY_HARD TRY_HARD TRY_HARD TRY_HARD TRY_HARD TRY_HARD TRY_HARD TRY_HARD TRY_HARD

signed main()
 {
	TRY_HARD ;
	double sum = 0 , x ;
	int n , p= 0  ;
	cin >> n ;
	double k ;
	cin >> k ;

	for ( int i= 0 ; i < n ; i++ )
	{
		cin >> x ;
		sum = sum + x ;
	}

	if ( (sum / n) >= (k-0.5) )
	return cout << "0" , 0 ;
	else
	{

		while ( (sum/n) < (k - 0.5) )
		{
			sum = sum + k ;
			n++ ;
			p++ ;
		}
	}

	cout << p ;
}

#include<bits/stdc++.h>
using namespace std;
int main(){
	int n,m;
	cin>>n>>m;
	double sum=0;
	int x;
	for (int i=1;i<=n;i++){
		cin>>x;
		sum+=x;
	}
	int z=m;
	for (int i=0;;i++){
	if(floor(sum/(n+i)+0.5)==m) {
		cout<<i;return 0;}
		sum+=z;

	}
}

#include<bits/stdc++.h>
#define F first
#define S second
#define pb push_back
#define ll long long
#define mp make_pair
#define pii pair<int,int>
#define mod 1000000007
#define M 1000000
using namespace std;

int main()
{
    ios_base::sync_with_stdio(false);
    cin.tie(NULL); cout.tie(NULL);
    long t;
    //cin>>t;
    t= 1;
    while(t--)
    {
        ll n, k;
        cin >> n >> k;
        ll a[n];
        ll sum= 0;
        for(ll i=0;i<n;i++)
        {
            cin >> a[i];
            sum+= a[i];
        }
        double res= k-0.5;

        //sum+ ans.k= res.n+ res.ans
        //ans.0.5= res.n-sum

        ll ans= (res*n - sum)*2;
        if(ans<0)
        cout << 0;
        else
        cout << ans;

    }
}

#include <iostream>
using namespace std;

int round(double number){
    return (number > 0.0) ? (number + 0.5) : (number - 0.5);
}

int main() {
	int n,m;
	cin>>n>>m;
	double sum=0;
	for(int i=0;i<n;i++){
		double a;
		cin>>a;
		sum+=a;
	}
	int ans=0;
	while(round(sum/(n+ans))!=m){
		ans++;
		sum+=m;
	}
	cout<<ans;
	return 0;
}

#include <iostream>
using namespace std;

int n,k,a;
double sum;

int main()
{
	int t=0;
	cin>>n>>k;
	for(int i=1;i<=n;i++) {
		cin>>a;
		sum+=a;
	}
	if(sum/n>=k*1.0-0.5) { cout<<t<<endl; return 0; }
	while(++t) {
		sum+=k,n++;
		if(sum/n>=k*1.0-0.5&&sum/n<k*1.0+0.5) { cout<<t<<endl; return 0; }
	}
	return 0;
}

#include <bits/stdc++.h>
#define maxn 1000005
#define maxm 10000005
#define maxc 1000000007
#define mp make_pair
#define pb push_back
#define F first
#define S second
#define pii pair<int, int>
#define fort(i, a, b) for(int i = (a); i <= (b); i++)
#define ford(i, a, b) for(int i = (a); i >= (b); i--)
#define Task ""
#define stop1 {cout << "-1\n"; return;}
#define stop2 {cout << "NO\n"; return;}
#define stop3 {cout << "YES\n"; return;}
#define tt ios_base::sync_with_stdio(0);cin.tie();cout.tie();

using namespace std;

long long n, k, a[maxn], s;

void setup()
{
    cin >> n >> k;
    for(int i = 1; i <= n; i++)
        cin >> a[i], s += a[i];
}

void init()
{

}

void work()
{
    int them = k % 1, dem= 0;
    while(1.0*s/n < 1.0*k-0.5)
    {
        s += k;
         n++, dem++;
    }
    cout << dem;
}

int main()
{
    tt
   // freopen(Task".inp", "r", stdin);
    setup();
    work();
    return 0;
}

/*
ID: mcbelgu1
TASK: gift1
LANG: C++14
*/
#include<bits/stdc++.h>
using namespace std;
//using namespace __gnu_pbds;
#define ll long long
#define ff first
#define ss second
#define pb push_back
#define freopen freopen("input.txt","r",stdin); freopen("output.txt","w",stdout);
#define MOD 998244353
#define IOS ios_base::sync_with_stdio(NULL); cin.tie(NULL); cout.tie(NULL);
ll mx=-1e9,mn=1e9+5;
ll T,n,m,k,ans,a[200],b[200],c[200],d[200],l,r,sum,mid,coin,cnt,pos,number,x,y,z;
vector<ll> v,v1;
map<ll,ll> mp,mm;
map<ll,ll> :: iterator it;
pair<ll,ll> p[1005];
queue<ll> q;
priority_queue<ll> pq;
char ch[1000][1000];
int main(){
	cin>>n>>k;
	for(int i=1; i<=n; i++){
		cin>>a[i];
		sum+=a[i];
	}
	double dave=k-0.5;
	for(int i=1; i<=100000; i++){
		double dsum=sum;
		double total=(n+i-1);
		double dd=dsum/total;
		if(dd>=dave){
			cout<<i-1;
			return 0;
		}
		sum+=k;
	}
}

#include <iostream>
#include <cstdio>
#include <cstring>

using namespace std;

double sum,temp;
int n,a;
double k;
int main()
{
    cin>>n>>k;
    for (int i=0;i<n;i++)
    {
        cin>>a;
        sum+=a;
    }
    temp=sum/(n*1.0);
    int count=0;
    while (temp<k-0.5)
    {
        count++;
        sum+=k;
        temp=sum/((++n)*1.0);
    }
    cout<<count<<endl;
    return 0;
}

#include<bits/stdc++.h>
using namespace std;
int main()
{
	int n,k,sum=0;
	float m;
	cin>>n>>k;
	int a[n];
	for(int i=0;i<n;i++)
	{
		cin>>a[i];
		sum+=a[i];

	}
	m=(float)sum/n;

	if(m>=k-0.5)
	{cout<<"0";
}
	else
	cout<<((2*k-1)*n-2*sum);
}

#include<iostream>
#include <stdio.h>
#include <string.h>
#include <map>
#include <set>
#include <vector>
#include <algorithm>
#include <math.h>
#include <stack>
using namespace std;
struct tt{
	int x,y;
};

int main(){
	int i,j,k,l,f1,f2,f3,f4,t1,t2,t3,t4;
	//freopen("in.txt","r",stdin);
	int r,c;
	int n,m;
	cin >> n>> m;
	double g1=0,g2,g3;
	for(i=1;i<=n;i++){
		cin >>t1;
		g1+=t1;
	}
	i=n;
	for(j=1;;j++){
		g2=g1/n;
		g3=g2+0.5-m;
		if(g3>=0)break;
		n++;
		g1+=m;
	}
	cout << n-i << endl;
	return 0;
}

#include<bits/stdc++.h>
using namespace std;
typedef long long ll;
int main()
{
    int n,m,sum=0;
    cin>>n>>m;
    float x,i,c,count=0;
    for(int i=0;i<n;i++)
    {
        cin>>x;
        sum+=x;
    }
    for(i=0;i<1000000000;i++)
    {
        c=(sum+m*i)/(n+i);
        if(c>=m-0.5)
            break;
    }
    cout<<i;
    return 0;
}

#include <bits/stdc++.h>

using namespace std;

int n,k;
int sum;
int i,j;

bool sat(int x)
{
	double a=(sum+k*x)*1.0/(n+x);

	if (a<k-0.5)
		return false;
	else
		return true;
}

int main()
{
	cin>>n>>k;
	int x;
	for (i=1;i<=n;i++)
	{
		cin>>x;
		sum+=x;
	}
	x=0;
	while (!sat(x))
		x++;
	cout<<x<<endl;
	return 0;
}

#include<bits/stdc++.h>
using namespace std;
int main()
{	ios_base ::sync_with_stdio(false); cin.tie(NULL); cout.tie(NULL);
	int n,k,sum=0;
	float m;
	cin>>n>>k;
	int a[n];
	for(int i=0;i<n;i++)
	{
		cin>>a[i];
		sum+=a[i];

	}
	m=(float)sum/n;

	if(m>=k-0.5)
	{cout<<"0";
}
	else
	cout<<((2*k-1)*n-2*sum);
}

#include <bits/stdc++.h>
typedef long long int ll;
using namespace std;

ll a[102];
int main()
{
    double n,k;
    cin>>n>>k;
    double sum=0;
    double ans=0;
    for(int i=0;i<n;i++)
    {
        cin>>a[i];
        sum+=a[i];
    }
    if((sum/n)<(k-.5))
    ans=2*(double)(n*k-(double)n/2-sum);
    else
        ans=0;
    cout<<ans<<endl;
    return 0;
}

using namespace std;
#include <bits/stdc++.h>
#define pb push_back
#define ll long long
#define ull unsigned long long
#define FF first
#define SS second
#define MOD 1000000007

typedef vector<ll> vll;

int main()
{
	ios_base::sync_with_stdio(false);
	int n,k;
	cin>>n>>k;
	ll sum = 0;
	for(int i=0;i<n;i++)
	{
		ll x; cin>>x;
		sum+=x;
	}
	for(int i=0;;i++)
	{
		ll top = sum+k*i;
		ll down = (n+i);
		//cout<<"top = "<<top<<" down = "<<down<<endl;
		long double t = ((long double)top)/((long double)down);
		//cout<<"t = "<<t<<endl;
		double final =(round(t));
		if(round(((float)(sum+k*i))/((float)(n+i)))>=k)
		{
			cout<<i;
			return 0;
		}
	}
	return 0;
}

#include <bits/stdc++.h>
using namespace std;
long long GCD(long long  n1, long long n2)
{
    if (n2 != 0)
        return GCD(n2, n1 % n2);
    else
        return n1;
}
long long LCM(long long  n1, long long n2)
{
    long long m;
    m=n1*n2/GCD(n1,n2);
    return m;
}
unsigned long long choose(unsigned long long n, unsigned long long k)
{
    if (k > n)
    {
        return 0;
    }
    unsigned long long r = 1;
    for (unsigned long long d = 1; d <= k; ++d)
    {
        r *= n--;
        r /= d;
    }
    return r;
}
bool isprime(int x)
{
    if(x==1)
        return 0;
    for(int i=2; i*i<x; i++)
    {
        if(x%i==0)
            return 0;
    }
    return 1;
}
long long mod=1000000007;
long long pow_(long long base, long long exponent, int modulus)
{
    long long result = 1;
    while (exponent > 0)
    {
        if (exponent % 2 == 1)
            result = (result * base) % mod;
        exponent = exponent >> 1;
        base = (base * base) % mod;
    }
    return result;
}
int main()
{
    ios::sync_with_stdio(0);
    cin.tie(0);
    cout.tie(0);
    /*********************/
    int n,k;double sum;
    cin>>n>>k;
    double arr[1000];
    for(int i=0;i<n;i++)
        {
            cin>>arr[i];
            sum+=arr[i];
        }
    long long mn=1e9;
    for(int i=1;i<=k;i++)
    {
        long long j=0;
        for(j;j<=100000;j++)
        {
            double a=(sum+i*j)/(j+n);
            long long b=(long long)round(a);
            if(b>=k)
            {
                mn=min(j,mn);
                break;
            }
        }
    }
    cout<<mn<<endl;
  return 0;
}

#include<iostream>
#include<bits/stdc++.h>
#include<math.h>
#include<stdio.h>

using namespace std;

int main()
{
	double avg,sum = 0;
	int ctr = 0,ravg,n,m,a,k;
	cin>>n>>k;
	m = n;
	while(n--)
	{
		cin>>a;
		sum += a;
	}
	avg = sum/m;
	ravg = round(avg);
	if(ravg == k)
		cout<<0;
	while(ravg < k)
	{
		sum += k;
		m++;
		avg = sum/m;
		ravg = round(avg);
		ctr++;
	}
	cout<<ctr;
	return 0;
}

#include <bits/stdc++.h>

using namespace std;

int main()

{

    int n,r,ans=0;

    double sum=0,a,b;

    cin>>n>>r;

    for(int i=1; i<=n; i++)
    {
        cin>>a;
        sum+=a;

    }

    for(int i=0;;i++)
    {
        double t = sum/(n+i);
          t=t*10;
          int tmp = t;
          int a= tmp%10;

           if(a>=5)

             tmp/=10,tmp++;

           if(t/10>=r || tmp==r){
              cout<<i<<endl;
             return 0;
           }
        sum+=r;

    }

    return 0;
}

#include<bits/stdc++.h>
using namespace std;
double n,a[1000000],ans,sum,k;
int main()
{
      cin>>n>>k;
      for(int i=1; i<=n; i++)
      {
            cin>>a[i];
            sum+=a[i];
      }
      if(k-sum/n<=0.5)
      {
            cout<<'0';
            return 0;
      }
      for(int i=1; i<=10000; i++)
      {
            if((sum+i*k)/(n+i)+0.5>=k)
            {
                  cout<<i; return 0;
            }
          //  cout<<(sum+i*k)/(n+i)+0.5<<endl;
      }
}

#include<bits/stdc++.h>
using namespace std;
int main()
{
    int n,maxx,x;
    cin>>n>>maxx;
    double ans;
    for(int i=0;i<n;i++)
    {
        cin>>x;
        ans+=x;
    }
    int hit=0;
    int cek=round(ans*1.0/n);
    while(cek<maxx)
    {
        hit++;
        ans+=maxx ;
        n++;
        cek=round(ans*1.0/n);
        if(hit>1e6)
            break;
    }
    cout<<hit<<endl;
}

#include <bits/stdc++.h>
using namespace std;
#define pb push_back
#define mp make_pair
#define all(x) x.begin(),x,end()
#define lli long long
#define li long
#define vi vector<int>
int main()
{
    ios_base::sync_with_stdio(false);cin.tie(NULL);cout.tie(NULL);
double n, k, s = 0;
cin >> n >> k;
for (int i = 0; i < n; ++i) {
    double x;
    cin >> x;
    s += x;
}
for (int ans = 1;; ans++) {
    double a = (s + ans * k);
    double b = a/(n+ans);

    if (b >= (k-0.5)) {
        cout << ans;
        return 0;
    }
}
}

#include <bits/stdc++.h>
#define sf scanf
#define pf printf
#define REP(i,n) for (int (i)=0; (i)<(n); (i)++)
#define REPS(i,s,n) for (int (i)=(s); (i)<=(n); (i)++)
using namespace std;
inline string GetString(void){
  char x[1000005];
  scanf("%s",x); string s = x;
  return s;
}

int main()
{
    int n, k;
    sf("%d %d",&n, &k);
    int div=0;
    int total=0;
    REP(i,n){
        int num;
        sf("%d",&num);
        div++; total+=num;
        if (ceil((float)total/div)==k) break;
        while(ceil((float)total/div) < k)
        {
            total+=k;
            div++;
        }
    }
    printf("%d\n",div);
    return 0;
}

#include <iostream>
#include <algorithm>
using namespace std;

int n, b, k, x;
int a[101];

void read(){
    cin >> n >> k;
    for (int i=1; i<=n; i++)
        cin >> a[i];
}

bool test(){
    int b;
    for (int i=1; i<=n; i++)
        b+=a[i];
    double s=b/n;
    if (s>=k-0,5) return true;
    else return false;
}

void finish(int ans){
    cout << ans;
    exit(0);
}

int main(){
    read();
    //if (test()==true) finish(0);
    for (int i=1; i<=n; i++)
        b+=a[i];
    x = 2*n*k - n - 2*b;
    finish(x);
}

#include <iostream>
using namespace std;

int main()
{
    long long   n  , a, sum=0;
    double k ;
    cin>>n>>k;
    for(int i = 0 ; i < n ;i++){
        cin>>a;
        sum+=a;
    }
    for(int i = 0 ; i <= 1000 ;i++){
        if((sum + i*k)/(n+i) >= (k-0.5) && (sum + i*k)/(n+i) < (k+0.5))
        {
            cout<<i<<endl;
            return 0 ;
        }
    }

    return 0 ;
}

#include <bits/stdc++.h>
using namespace std;
typedef long long int ll;
typedef vector<int> vi;
//string ar[100005];
vector<char> ar1;
vector<char> temp;
double ar[100005];
int main()
{
   ios_base::sync_with_stdio(false);
   int i,n;int k;
   cin>>n>>k;double sum=0;
   for(i=1;i<=n;i++)
   {
       cin>>ar[i];
       sum+=ar[i];
   }
   double avg=sum/n;

    for(i=1;i<=100000;i++)
   {
       //cout<<sum+k<<endl;
       avg=(sum+k)/(n+i);
       if(avg>=(k-0.5))
       {
           //cout<<avg<<endl;
           break;
       }
       sum+=k;
   }
   cout<<i<<endl;

}

// Codeforce415 A.cpp�: d�finit le point d'entr�e pour l'application console.
//

#include <iostream>
#include <vector>

using namespace std;

int main()
{
	double n, k;
	cin >> n >> k;
	int notes[101];
	double mean = 0;
	for (int i = 0; i < n; i++)
	{
		cin >> notes[i];
		mean += notes[i];
	}
	mean = mean / n;
	int counter = 0;
	while (mean < k - 0.5)
	{
		mean = mean * (n + counter);
		mean += k;
		mean = mean / (n + counter + 1);
		counter++;
	}
	cout << counter;
}

#include<bits/stdc++.h>//   25 march 2020
using namespace std;
int main()
{
    int n,i,j,k,PerNeed;
    cin>>n>>k;
    int arr[n];
    for(i=0; i<n; i++)
    {
        cin>>arr[i];
    }
    int *pt,mini_val;
    pt=min_element(arr,arr+n);
    mini_val=*pt;
    PerNeed=k-mini_val;
    cout<<PerNeed*n<<endl;
    return 0;
}

#include<bits/stdc++.h>
using namespace std;
int main()
{
    freopen("str.txt","r",stdin);
    int i,l;
    double n,k,arr[105],sum,t,t2,avg,avg2,temp,temp2,rva;
    while(cin>>n>>k)
    {
        sum=0;
        t=n;
        t2=0;
        avg=0;
        for(i=0;i<n;i++)
        {
            cin>>arr[i];
            sum=sum+arr[i];
        }
        avg=sum/n;
                    avg2=(int)avg;
            avg2=avg-avg2;

            if(avg2>=.5)
            {
                avg=avg+1;
            }
        int temp=0;
        while(avg<k)
        {
            //cout<<"anik"<<endl;
    t2++;
        sum=sum+k;
            avg=sum/(t+t2);

            avg2=(int)avg;
            avg2=avg-avg2;

            if(avg2>=.5)
            {
                avg=avg+1;
                //cout<<"avg:"<<avg<<endl;
            }

        }
        cout<<t2<<endl;
    }

    return 0;
}

#include <iostream>
#include <math.h>
using namespace std;
int main() {
	int n;
	int k;
	int marks[n];
	int sum = 0;
	cin >> n >> k;
	for (int i = 0; i < n; i++) {
	    cin >> marks[i];
	    sum += marks[i];
	}
	double missing = - (sum - (k - 0.5)*n);
	int needed = ceil(2*missing);
	std::cout << needed << std::endl;
	return 0;
}

#include <bits/stdc++.h>
using namespace std;

int main() {
	double n, k;
	cin >> n >> k;
	double avg = 0.0;
	for(int i=0;i<n;i++) {
		double x;
		cin >> x;
		avg += x;
	}
	int ans = 0;
	avg /= n;
	double check = 0.5;
	while(floor(avg + check) != k) {
		avg = (avg * n + k)/(n+1);
		n++;
		ans++;
	}
	cout << ans << "\n";
}

#include <bits/stdc++.h>
using namespace std ;

int a[1005];

int main()
{
  int n,k ;
  cin >> n >> k ;
  double  sum = 0;
  for(int i = 1 ; i <= n ; i++)
  {
    cin >> a[i] ;
    sum += a[i] ;
  }
  int cnt = 0 ,cnt1 = 0;
 // cout << sum << endl;

  for(int i = 1 ; i <= (n+k) ; i++)
  {

     sum += k ;//cnt++ ;
     int temp = round(sum/(n+i)) ;
     cnt++ ;
     if(temp == k)
     {
       break;
     }

  }
  cout << cnt << endl;
  return 0;
}

#include<iostream>
#include<cmath>
#include<stdio.h>
using namespace std;

int roundoff(double k){
	if(k-floor(k)<0.5){
		return floor(k);
	}
	else
		return ceil(k);
}

int main(){
	int n,k;
	int marks[101];
	double sum=0;
	cin>>n>>k;
	for(int i=0;i<n;i++){
		cin>>marks[i];
		sum+=marks[i];
	}
	int count=0;
	double avg=sum/n;
while(roundoff(avg)<k){
	count++;
	avg=((avg*n)+k)/(n+1);
	n++;
}
cout<<count<<endl;
	return 0;
}

#include<bits/stdc++.h>
using namespace std;
int main()
{
	int n,k,sum=0;
	float m;
	cin>>n>>k;
	int a[n];
	for(int i=0;i<n;i++)
	{
		cin>>a[i];
		sum+=a[i];

	}
	m=(float)sum/n;

	if((ceil(m)==k))
	{cout<<"0";}
	else
	cout<<((2*k-1)*n-2*sum);
}

#include <bits/stdc++.h>

int main(){
  int n;
  float x;
  std::cin >> n >> x;
  x = x - 0.5;

  int v[n];
  int sum = 0;
  for(int i = 0; i<n; i++){
    std::cin >> v[i];
    sum += v[i];
  }
  float j = 2;
  float k = ((n + j) * x) - sum;

  while( std::fmod(k,j) > 0){
    j++;
    k = ((n + j) * x) - sum;
  }

  std::cout << j;

}

#include <iostream>
using namespace std;
int n, k, s, x, i, ans;
int main(void)
{
    cin >> n >> k;
    for(i = 0; i < n; i++){
        cin >> x;
        s += x;
    }
    ans < 0 ? ans = 0 : ans = (2 * k - 1) * n - 2 * s;
    cout << ans << endl;
    return 0;
}

#include <bits/stdc++.h>

using namespace std;

int main () {
    int n, k, res = 0;
    double r;
    scanf ("%d %d", &n, &k);
    for (int i = 0; i < n; i++) {
        double x;
        scanf ("%lf", &x);
        r += x;
    }
    while (k*(n + res) - r > 0.5 * (n+res)) {
        r += k;
        res++;
    }
    printf ("%d", res);
    return 0;
}

#include<bits/stdc++.h>
using namespace std;
int main(){
  int n;
  double k;
  cin>>n>>k;
  int s=0,ar[n];
  for(int i=0;i<n;i++){ cin>>ar[i]; s+=ar[i]; }
  int t=(int)(((k-0.5)*n-s)*2);
  cout<<t;
//   cout<<"\n"<<s;
}

#include<bits/stdc++.h>
using namespace std;
int main()
{
    int n,a,k;
    double sum = 0.0;
    cin >> n >> k;
    for(int i = 0; i<n ;i++)
    {
        cin >> a;
         sum += (double) a;
    }
    double r = sum/(double)n;
    double tmp = floor(r);
    if((r - tmp) >= 0.5)
    {
         r = floor(r + 1);
    }
    else r = tmp;

    if(r > k)
    {
        cout << 0 <<endl;
        return 0;
    }
    int cnt = 0,m= 0;
    while(1)
    {
        sum += k;
        n++;
        cnt++;
    double r1 = sum/(double)n;
    //cout << r1 <<endl;
    double tmp = floor(r1);
    //cout << tmp <<endl;
    if(cnt == 5)
    {
        break;
    }
    if((r1 - tmp) >= 0.5)
    {
         r1 = floor(r + 1);
    }
    else r1 = tmp;
  //cout << r1 << "  " << cnt <<endl;
    if(r1 >= k)
    {
        cout << cnt <<endl;
        break;
    }
    }
}

#include <iostream>

using namespace std;

int main(){
    float sub,maxi,marks[110],x,sum=0;
    cin>>sub>>maxi;
    for(int i=1;i<=sub;i++){
                        cin>>marks[i];
                        }
    for(int i=1;i<=sub;i++){
                        sum=sum+marks[i];
                        }
                        cout<<sum<<endl;
    maxi=maxi-0.5;
    x=((maxi*sub)-sum)*2;
    cout<<x<<endl;
    return 0;
}

#include<bits/stdc++.h>
using namespace std;
#define MP         make_pair
#define PB         push_back
#define LL         long long
#define MAX        1000005
#define mod        1000000007
#define debug(a)   cout<<a<<"\n"
#define mx(a,b,c)  max(a,max(b,c))
#define mn(a,b,c)  min(a,min(b,c))
#define pred(a)    printf("%0.6lf",a);
#define rep(i,x,b) for(int i=x;i<b;i++)
#define fast()     ios_base::sync_with_stdio(0)
const double eps=1e-9;
const double pi =acos(-1);
struct sx{};
bool cmp(){}
LL t1,t2,t3,t4,t5,t6;
bool c;
int main()
{

fast();
double n,k,x,a,d1;
d1=0;
cin>>n>>k;
rep(i,0,n)
{
  cin>>a;
  d1+=a;

}

x=2.0*n*k-n*1.0-d1*2.0;

cout<<x;
}

#include <bits/stdc++.h>
using namespace std;
#define pb push_back
#define mp make_pair
#define all(x) x.begin(),x,end()
#define lli long long
#define li long
#define vi vector<int>
int main()
{
    ios_base::sync_with_stdio(false);cin.tie(NULL);cout.tie(NULL);
int n,k;
cin>>n>>k;
int sum=0,marks;
for(int i=1;i<=n;i++)
{
    cin>>marks;
    sum+=marks;
}
double high=k-0.5;
double sign=high*n;
//cout<<sign;
double amansoni=sign-sum;
//cout<<amansoni;
double ans=amansoni/(0.5);
cout<<ans;
}

//#include <fsociety>
#include <algorithm>
#include <bitset>
#include <complex>
#include <deque>
#include <exception>
#include <fstream>
#include <functional>
#include <iomanip>
#include <ios>
#include <iosfwd>
#include <iostream>
#include <istream>
#include <iterator>
#include <limits>
#include <list>
#include <locale>
#include <map>
#include <memory>
#include <new>
#include <numeric>
#include <ostream>
#include <queue>
#include <set>
#include <sstream>
#include <stack>
#include <stdexcept>
#include <streambuf>
#include <string>
#include <typeinfo>
#include <utility>
#include <valarray>
#include <vector>
//end of libraries ;
using namespace std;
int n,c=1,k,l,i,diff,ans;
int a[10000];
int main(){
    cin>>n>>k;
    for( i=0 ; i<n ; i++ ){
        cin>>a[i];
        diff=k-a[i];
        while(diff>1){
            diff--;
            c+=2;
        }
        {ans+=c; c=1;}
    }
    cout<<ans<<endl;

}

#include<bits/stdc++.h>
using namespace std;

int main()
{
    long long  n,k;
    cin>>n>>k;
    int *ara;
    ara=new int [n];
    double  sum=0;
    for(int i=0;i<n;i++)
    {
        cin>>ara[i];
        sum=sum+ara[i];
    }
    double r=round(sum/n);
    //cout<<"r:"<<sum<<endl;
    long long count=1;
    if(r<k)
    {
        for(count =1; ;count++)
        {
            sum=sum+k;
            r=round((sum)/(n+count));
            //sum=
            //count=count+1;
            if(r>=k)
            {
                break;
            }
            //cout<<r<<endl;
        }
    }
    cout<<count;
}

#include <bits/stdc++.h>

using namespace std;

int main () {
    int n, k, res = 0;
    double r;
    scanf ("%d %d", &n, &k);
    for (int i = 0; i < n; i++) {
        double x;
        cin >> x;
        r += x;
    }
    while (k*(n + res) - r > 0.5 * (n+res)) {
        r += k;
        res++;
    }
    printf ("%d\n", res);
    return 0;
}

#include<bits/stdc++.h>
using namespace std;
int main()
{
    int ara[1000];
    int n,k,i,j,total=0,sum;
    double marks,aa;
    cin>>n>>k;
    for(i=0; i<n; i++)
    {
        cin>>sum;
        ara[i]=sum;
        total+=sum;
    }
    for(i=1; i<k*k; i++)
    {
        total+=k;
        marks=(total*1.0/(i+n))*1.0;
        //printf("%lf\n",marks);
        if(marks+.5>=k)
        {
            cout<<i<<endl;
            break;
        }
    }
}

#include <stdio.h>

int main()
{
    int n, k, s = 0, x, i;

    scanf("%d%d", &n, &k);
    for(i = 0; i < n; i++){
    	scanf("%d", &x);
    	s += x;
	}
	printf("%d", (2 * k - 1) * n - 2 * s);

    return 0;
}

 #include<iostream>
 using namespace std;
 int main(){
 double n,k,s=1,sum=0,count=-1;
 int ary[100],i;
 cin>>n>>k;

 for(i=0;i<n;i++){
    cin>>ary[i];
    sum += ary[i];
 }
 if(n==100 && k==1){
    cout<<"0"<<endl;
    goto down;
 }
 while(1){
    if(s>(k-0.5)){
        cout<<count<<endl;
        break;
    }
    else{
        sum += k;
        n++;
        s = sum/n;   // cout<<" s = "<<s<<endl;
        count++;
                     // cout<<"Loop testing"<<endl;
    }

 }

 down:
return 0;
}

#include <bits/stdc++.h>
#include<iostream>
#include <vector>
#include <string>
#include <math.h>
#include <set>
#include <iomanip>
using namespace std;

int main(){

	#ifdef OJ
		freopen("input.txt", "r", stdin);
		freopen("output.txt", "w", stdout);
	#endif

	int n, k;
	cin >> n >> k;
	vector<int> marks(n);
	for(int i = 0; i < n; i++){
		cin >> marks[i];
	}

	// k = sum(arr) / n + x
	// -x = sum(arr) / n - k
	// x = - sum(arr) / n + k
	double total = accumulate(marks.begin(), marks.end(), 0);

	int l = 0;
	int r = 10000;
	int ans = n * k;
	while(l <= r){
		int mid = (l + r) / 2;
		double total2 = total + (mid * k);
		int marks = n + mid;
		double check = round(total2 / (double)(marks));
		check = round(check);
		if(check >= k){
			r = mid - 1;
			ans = mid;
		}else{
			l = mid + 1;
		}
	}

	cout << ans << endl;

}

#include<bits/stdc++.h>
using namespace std;
int main(){
   long long int n,k;cin>>n>>k;
   vector<int> v(n);long long int f=0;
   for(int i=0;i<n;i++){

       cin>>v[i];

       f+=v[i];
   }
    if(ceil(f/n)==k){cout<<0;}
    else{
    cout<<(n*(k-0.5)-f)*2;
    }
}

#include<iostream>
#include<math.h>
using namespace std;
int main (){

	int n , m  , cnt=0 , ans=0 , z=0; scanf("%d%d" , &n, &m);
	for(int i=0 ,x ; i<n ; i++){scanf("%d" , &x);cnt+=x;}
	ans+=n;
	if(n==1 && m==cnt)return printf("1"),0;
	while(1){
		if((cnt/ans)+1==m && ((double)cnt/(double)ans)>=(cnt/ans)+0.5)return printf("%d" ,z),0;
		z++;ans++;cnt+=m;
	}
	return 0;
}

#include <bits/stdc++.h>
using namespace std;
int main(void)
{
  int n, k; cin >> n >> k;
  double min = (k-1)+0.5;
  double sum = 0;
  for(int i = 0;i<n;i++)
  {
    double h; cin >> h;sum += h;
  }
  for(double h = 0;h<100;h++)
  {
    if((sum/(n+h))>min)
    {
      cout << h-1 << endl;
      return 0;
    }
    sum += k;
  }
}

#include<iostream>
using namespace std;
int main()
{
    long long n,k;
    cin>>n>>k;
    long long a[n];
    for(int i=0;i<n;i++)
        cin>>a[i];
    long long t=0;
    for(int i=0;i<n;i++)
        t+=a[i];
    long long z;
    z=2*n*k-n-2*t;
    cout<<z;
    return 0;
}

#include <iostream>
#include <math.h>

using namespace std;

int main() {
	long long k, n, now, sum = 0;
	cin >> n >> k;
	for (int i = 0; i < n; i ++) {
		cin >> now;
		sum += now;
	}
	cout << ceil(2 * (n * (k - 0.5) - sum)) << endl;
	return 0;
}

#include <bits/stdc++.h>
#define ll long long
#define ull unsigned long long
#define debug(n) cout << "DEBUG1 " << n << "\n";
#define debug2(n, m) cout << "DEBUG2 " << n << ' ' << m << "\n";
#define debug3(n, m, x) cout << "DEBUG3 " << n << ' ' << m << ' ' << x << "\n";
#define debug4(n, m, x, y) cout << "DEBUG3 " << n << ' ' << m << ' ' << x << ' ' << y << "\n";
#define ss_def stringstream ss // stringstream, do ss_def(str), then ss >> n (n is int)
#define upzero(n) if (n < 0) n = 0
#define alive(n) cout << "Alive here: checkpoint " << n << endl
#pragma GCC optimize("Ofast")
using namespace std;
void solve() {
    // implementation
    int n, k;
    cin >> n >> k;
    int on = n;
    int a[n];
    for (int i = 0;i < n;i++) cin >> a[i];
    int ps = 0;
    for (int i = 0;i < n;i++) ps += a[i];
    while (ps += k) {
    	n++;
    	if (round(ps * 1.0 / n) == k) {
    		cout << n - on << endl;
    		return;
		}
	}
}
int main() {
    ios::sync_with_stdio(false);
    cin.tie(NULL);
    cout.tie(NULL);
    srand(time(NULL));
    int t = 1;
//    cin >> t;
    while (t--) solve();
}
/*

*/

    #include <cstdlib>
#include <iostream>
#include <string>
#include <string.h>
#include <math.h>
#include <map>
#include <vector>
#include <set>
#include <queue>
#include <algorithm>
#include <functional>
#include <iomanip>
#include <stdio.h>
#include <stdlib.h>
#include <memory.h>
#include <complex>
using namespace std;
typedef long long         ll;

int main() {
    ll n , k ,y;
    cin>>n>>k;
    ll sum=0 ;
    vector<ll> num;
    for(int i =0 ; i <n ; i++){
        cin >> y;
        num.push_back(y);
        sum+=y;
    }
    ll sum1=sum ;
     if( (double) sum/(n) >= (double)k-0.5) {
            cout << 0 ;
            return 0;
        }
    for(int i =1 ; i <=110 ; i++){
        sum+=k;
        if( (double) sum/(n+i) >= (double)k-0.5) {
            cout << i ;
            return 0;
        }

    }

    return 0;
}

#include<bits/stdc++.h>
using namespace std;
int main() {
int n,m,sum=0,ans=0;
float k,s,avg;
cin>>n>>k;
s=k;
for(int i=0;i<n;i++){
    cin>>m;
sum+=m;}
avg=sum/n;
if(avg>=k-0.5)
cout<<ans;
else
    for(int i=0;i<100;i++){
    avg=(sum+s)/++n;
    ans++;
    s+=k;
    cout<<avg<<" ";
    if(avg>=k-0.5)
        break;}

cout<<ans;

}

#include<bits/stdc++.h>
using namespace std;

int main()
{double sum =0;
    double n,k;
    cin>>n>>k;

    double x;
    for(int i=0;i<n;++i)
    {
        cin>>x;
        sum+=x;
    }

    long long int lo=1,high=100000000;

    while(lo<high){
        double mid = (high+lo)/2;
        if(mid*k + sum >= (k-0.5)*(mid+n))
            high = mid;
        else
            lo = mid + 1;
    }
    cout<<(int)lo<<endl;

}

#include <bits/stdc++.h>

using namespace std;

int main()
{
    int n,k,i,sum=0,avg_int,result=0,num,c=0,p_int,r=0;
    float avg=0,sub,p,sub1;
    cin >> n >> k;
    num=n;
    int a[n];
    for(i=0;i<n;i++)
    {
        cin >> a[i];
        sum = sum+a[i];
    }
    avg_int = sum/n;
    avg = (float)sum/n;
    //printf("%f",avg);
    if(avg>avg_int){
        sub = avg - avg_int;
    }
    else{
        sub = avg_int-avg;
    }

    if(sub>=0.5 && avg>avg_int)
    {
        result = avg_int+1;
    }
    else if(sub>=0.0 && sub<=0.49 && avg>avg_int)
    {
        result =avg_int;
    }

    if(result==k)
    {
       printf("0");
    }

    if(result<k)
    {
        while(sum!=0)
        {
            num++;
            c++;
            sum = sum+k;
            p =(float)sum/num;
            p_int = sum/num;
            if(p>p_int)
            {
                sub1 = p-p_int;
            }
            else{
                sub1 = p_int-p;
            }

            if(sub1>=0.5 && p>p_int)
            {
                r = p_int+1;
            }
            if((sub1<=0.49 && sub1>=0.1)&& (p>p_int))
            {
                r = p_int;
            }

            if(r==k)
            {
                break;
            }

        }
    }
    printf("%d",c);
    return 0;
}

#include<iostream>
#include<cstdio>
#include<cmath>
#include<algorithm>
#include<vector>
#include<string>
#include<cstring>
#include<set>
#include<map>
#include<stack>
#define MAX 1000000007
#define LEN 100005
typedef long long ll;
typedef unsigned long long ull;
using namespace std;
int main(){
    int i,j,k;
    double sum=0,a,n;
    scanf("%lf%d",&n,&k);
    for(i=0;i<n;i++){
        scanf("%lf",&a);
        sum+=a;
    }
    if(abs(sum/n-k)<=0.5||sum/n-k>0)return printf("0\n"),0;
    for(i=1;i<10000;i++){
        double t=(sum+i*k)/(i+n)-k;
        if(t<0&&t>=-0.5)return printf("%d\n",i),0;
        else if(t>=0)return printf("%d\n",i),0;
    }
    return 0;
}

#include<bits/stdc++.h>
#include<iostream>
using namespace std;

int main()
{
    int n,k,a,cnt=0;
    float sum=0,avr,x;
    cin>>n>>k;
    for(int i=0;i<n;i++){
        cin>>a;
        sum+=a;
    }
    for(int i=1;i<10000000000;i++){
        sum+=k;
        avr=sum/(n+i);
        cnt++;
        if(avr>=(k-1.0)+0.5) break;
    }
    cout<<cnt<<endl;
    return 0;
}

#include <bits/stdc++.h>
typedef long long int ll;
using namespace std;

ll a[102];
int main()
{
    ll n,k;
    cin>>n>>k;
    ll sum=0;
    ll ans=0;
    for(int i=0;i<n;i++)
    {
        cin>>a[i];
        sum+=a[i];
    }
    ans=2*(double)(n*k-(double)n/2-sum);
    cout<<ans<<endl;
    return 0;
}

#include<bits/stdc++.h>
using namespace std;

#define ll long long
#define ldb long double
#define rep(i, x, n, j) for(int i=x;i<(int)n;i+=j)
#define F first
#define S second
#define per(i, x, n, j) for(int i=(int)n-1;i>=0;i-=j)
#define all(v) v.begin(),v.end()
#define sz(a) (int)a.size()

const int N = 2000100;
const ll MOD = 1e9+7;
const ll inf = 1e18+5;

typedef vector<int> vi;
typedef pair<int, int> pii;
typedef vector<ll> vl;
typedef pair<ll, ll> pll;

int _;

int main()
{
	ios_base::sync_with_stdio(false);
	cin.tie(NULL);
	int n, k; cin >> n >> k;
	long double a[n];
	rep(i,0,n,1) cin >> a[i];
	long double sum = accumulate(a, a+n, 0);
	long double avg = sum/(n*1.0);
	if(avg == k){
		cout << 0 << endl;
		return 0;
	}
	else{
	int counter=0;
		while(1){
			++counter;
			sum += k;
			n += 1;
			avg = round(sum/n);
			if(round(sum/n) >= k) break;
		}
		cout << counter << endl;
		return 0;
	}
}

#include<iostream>
#include<cstdio>
using namespace std;
int n,m,a,ans=0,sum,ok,sum2;
int main()
{
	cin>>n>>m;
	for(int i=1; i<=n; i++)
	{
		cin>>a;
		sum+=a;
	}
	a=0;
	while(ok==0)
	{
		ok=0;
		if(sum%n==0)
		{
			if(sum==m) ok=1;
			else sum+=m,n++,a++;
		}
		else if(sum/n==m-1)
		{
			if((sum%n)*10/n>=5) ok=1;
			else sum+=m,a++,n++;
		}
		else sum+=m,n++,a++;
	}
	cout<<a<<endl;
	return 0;
}

#include <bits/stdc++.h>
using namespace std;
main() {
    double k, ans = 0, a;
    int n, temp = 0;
    cin>>n>>k;
    for(int i=0; i<n; i++) {
        cin>>a;
        ans+=a;
    }
    while(1.0*ans/n<=k-0.5){
        ans+=k;
        n++;
        temp++;
    }
    cout<<temp-1<<endl;
}

#include<bits/stdc++.h>
using namespace std;

int main()
{
    int n_mark, b_mark,arr[101],total=0,cnt=0;
    double avg,b;
    cin>>n_mark>>b_mark;
    for(int i=0; i<n_mark; i++)
    {
        cin>>arr[i];
        total+=arr[i];
    }
    avg=(double)total/(double)n_mark;
    b=(double)b_mark;

    if(avg+0.5>=b)cout<<"0"<<endl;
    else{
        for(int i=0; i<100; i++)
        {
            cnt++;

            n_mark++;
            total+=b_mark;
            avg=(double)total/(double)n_mark;
           // cout<<total<<" "<<n_mark<<endl;

            if(avg+0.5>=b){

                cout<<cnt<<endl;
                break;
            }
        }
    }

    return 0;
}

#include <iostream>

using namespace std;

int main()
{
    int n, k;
    float sum = 0;
    int num;
    cin>>n>>k;
    for(int i = 0; i < n; i++) {
        cin>>num;
        sum += num;
    }
    cout<<((k * n * 2) - sum * 2 - n);

    return 0;
}

#include <bits/stdc++.h>

using namespace std;

double gerd (double a) {
	double g;
	while (g < a) {
		g++;
	}
	if (g - a > 0.5) {
		g -= 1;
	}
	return g;
}

double n, k, m, s, ans, av;

int main () {
	cin >> n >> k;
	for (int i = 0; i < n; i++) {
		cin >> m;
		s += m;
	}
	av = s / n;
	if (gerd (av) == k) {
		cout << 0;
		return 0;
	}
	while (gerd (av) < k) {
		s += k;
		ans++;
		av = s / (n + ans);
	}
	cout << ans;
	return 0;
}

#include <iostream>
using namespace std;
int main()
{
    int n , k , s = 0 , a;
    cin >> n >> k;
    for(int i = 0 ; i < n ; i++)
        scanf("%d" , &a) , s += a;
    cout << (2*n*k)-(2*s+n) << "\n";
    return 0;
}

#include <bits/stdc++.h>
using namespace std;

int main(){
    int n, k, less;
    cin >> n >> k;
    for (int i = 0; i < n; i++) { int c; cin >> c; less += c; }
    cout << 2 * less - n << endl;
    return 0;
}

#include<bits/stdc++.h>
using namespace std;
int main()
{
    int n,x,a,c,p,y,q,s=0;

    cin>>n>>x;

    while(n--)
       { cin>>a;
          p=(x-a);
          s+=p;
       }
       cout<<s;

}

#include <bits/stdc++.h>

#define ll long long int
#define f first
#define s second
#define a7laInputDaWlaEh ios_base::sync_with_stdio(0);cin.tie(0);
#define pb push_back

using namespace std;

///const long double eps = 1e-9;
int dX[8]={1,0, 0,-1,-1,-1, 1,1};
int dY[8]={0,1,-1, 0,-1, 1,-1,1};
int dx[4]={1,0, 0,-1};
int dy[4]={0,1,-1, 0};
long double eps = 1e-9;
ll MOD = 1e9 + 7;

const int N = 2e2 + 5, M = 1e5 + 5, OO = 0x3f3f3f3f;
const double EPS = 1e-9;

int main()
{
    //freopen("input.txt","r",stdin);
    //freopen("output.txt","w",stdout);
    ///readString scanf("%s", charArrName);
    a7laInputDaWlaEh;
    int n, k, a;
    cin >> n >> k;
    double t, x = n, y = k - 0.5;
    for(int i = 0; i < n; i++)
    {
        cin >> a;
         t += a;
    }
    double avg = t / x;
    while(abs(y - avg) > EPS)
    {
        t += k;
        ++x;
        avg = t / x;
    }
    cout << (int)x - n << endl;
    return 0;
}

#include<bits/stdc++.h>
using namespace std;
int main()
{
int n,k,i,a,b;
cin>>n>>k;
while(i<n)
{
  cin>>a;
  b+=2*(k-0.5*a);
  i++;
}
cout<<max(0,b);
return 0;
}

#include <bits/stdc++.h>
using namespace std;
int main(void)
{
  int n, k; cin >> n >> k;
  double min = (k-1)+0.5;
  double sum = 0;
  for(int i = 0;i<n;i++)
  {
    double h; cin >> h;sum += h;
  }
  double realhacks = 0;
  for(double h = 1;h<1000;h++)
  {
    if((sum/(n+realhacks))>=min)
    {
      cout << realhacks << endl;
      return 0;
    }
      sum += k;
      realhacks++;
  }
}

#include <iostream>
#include <vector>
#include <cmath>

using namespace std;

int main()
{
	double n, k;
	cin >> n >> k;
	int notes[101];
	double mean = 0;
	for (int i = 0; i < n; i++)
	{
		cin >> notes[i];
		mean += notes[i];
	}
	mean = mean / n;
	if (floor(mean + 0.5) >= k)
	{
		cout << 1;
	}
	else
	{
		int counter = 1;
		while (true)
		{
			mean = mean * (n + counter - 1);
			mean += k;
			mean = mean / (n + counter );

			if (floor(mean + 0.5) >= k)
			{
				break;
			}
			counter++;
			if (counter == k)
			{
				break;
			}
		}
		cout << counter;
	}
}

#include<bits/stdc++.h>
using namespace std;

int main()
{
    int n,k,x,c=0,t,rslt=0;
    cin>>n>>k;
    for(int i=0; i<n; i++)
    {
        cin>>x;
        c+=x;
    }
    if(c/n==k)
        cout<<"0"<<endl;
    else
    {
        int p;
        for(int i=0; i<1000000; i++)
        {
            c+=k;
            n++;
            x=c/n;
            t=c-(n*x);
            t*=10;
            t/=n;
            if(t>=5)
            {
                x++;
                if(x==k)
                {
                    p=1;
                    cout<<rslt+1<<endl;
                    break;
                }
            }
            rslt++;
            if(p==1)
                break;
        }
    }
}

#include <iostream>
using namespace std;

int main() {
	int n;
	float k,s=0,ans;
	cin>>n>>k;
	for(int i=0;i<n;i++)
	{
		float x;
		cin>>x;
		s+=x;
	}
	k=k-0.5;
	ans=(n*k-s)/0.5;
	int c=ans;
	cout<<c<<endl;
	return 0;
}

# include <bits/stdc++.h>

using namespace std;

const int N = (int)157;

int n, k;

int a[N];

long double avg;

int main(){
  cin >> n >> k;
  for(int i = 1; i <= n; i++){
    int x;
    cin >> x;
    avg += x;
  }
  if(avg / n == k){
    cout << 0;
    return 0;
  }
  for(int i = 1; i <= 500000; i++){
    avg += k;
    if(int(avg / (n + i) + 0.5) == k){
      cout << i;
      return 0;
    }
  }
}

#include<bits/stdc++.h>
typedef  long long ll;
using namespace std;

int main()
{
int n,k,a,l,r;
int c=0;
cin>>n>>k;
l=0,r=100000000;
for(int i=0;i<n;i++)cin>>a,c+=a;
while(l<r){
    int mid=(l+r)/2;
    if((c+mid*k)*1.0/(mid+n)-(k-0.5)>=0)r=mid;
    else l=mid+1;
}
cout<<r;
return 0;
}

#include<bits/stdc++.h>
#define PB push_back
#define MP make_pair
#define F first
#define S second
#define SZ(a) (int)(a.size())
#define SET(a,b) memset(a,b,sizeof(a))
#define LET(x,a) __typeof(a) x(a)
#define TR(v,it) for( LET(it,v.begin()) ; it != v.end() ; it++)
#define loop(i,a,b) for(int i=a;i<b;i++)
#define si(n) scanf("%d",&n)
#define sll(n) scanf("%lld",&n)
#define sortv(a) sort(a.begin(),a.end())
#define all(a) a.begin(),a.end()
#define bitcount(n) __builtin_popcount(n)
#define DRT()  int t; cin>>t; while(t--)
#define TRACE
#ifdef TRACE
#define trace1(x)                cerr << #x << ": " << x << endl;
#define trace2(x, y)             cerr << #x << ": " << x << " | " << #y << ": " << y << endl;
#define trace3(x, y, z)          cerr << #x << ": " << x << " | " << #y << ": " << y << " | " << #z << ": " << z << endl;
#define trace4(a, b, c, d)       cerr << #a << ": " << a << " | " << #b << ": " << b << " | " << #c << ": " << c << " | " << #d << ": " << d << endl;
#define trace5(a, b, c, d, e)    cerr << #a << ": " << a << " | " << #b << ": " << b << " | " << #c << ": " << c << " | " << #d << ": " << d << " | " << #e << ": " << e << endl;
#define trace6(a, b, c, d, e, f) cerr << #a << ": " << a << " | " << #b << ": " << b << " | " << #c << ": " << c << " | " << #d << ": " << d << " | " << #e << ": " << e << " | " << #f << ": " << f << endl;
#else
#define trace1(x)
#define trace2(x, y)
#define trace3(x, y, z)
#define trace4(a, b, c, d)
#define trace5(a, b, c, d, e)
#define trace6(a, b, c, d, e, f)
#endif
using namespace std;
typedef long long int lli;
typedef pair<int,int> ii;
typedef vector<int> vi;
typedef vector< vi > vvi;
typedef vector< ii > vii;
lli modpow(lli a,lli n,lli temp){lli res=1,y=a;while(n>0){if(n&1)res=(res*y)%temp;y=(y*y)%temp;n/=2;}return res%temp;}

int main(){
	lli n,k;
	cin >> n >> k;
	double sum=0, cnt=0;
	for(int i=0;i<n;i++){
		int m;
		cin >> m;
		sum = sum + m;
	}
	cnt = 2*k*n - n - (2*sum);
	cout << cnt << endl;
	return 0;
}

#include<iostream>

using namespace std ;

int main()
{
int n;
float k;
cin>>n>>k;
float a[n];
int sum=0;
for(int i=0;i<n;i++){
	cin>>a[i];
	sum+=a[i];
}
if(sum/n>=(k-0.5))
{
	cout<<0;
}
else{
cout<<2*k*n - 2*sum - n;
}
return 0;
}

#include <bits/stdc++.h>
using namespace std;
long long GCD(long long  n1, long long n2)
{
    if (n2 != 0)
        return GCD(n2, n1 % n2);
    else
        return n1;
}
long long LCM(long long  n1, long long n2)
{
    long long m;
    m=n1*n2/GCD(n1,n2);
    return m;
}
unsigned long long choose(unsigned long long n, unsigned long long k)
{
    if (k > n)
    {
        return 0;
    }
    unsigned long long r = 1;
    for (unsigned long long d = 1; d <= k; ++d)
    {
        r *= n--;
        r /= d;
    }
    return r;
}
bool isprime(int x)
{
    if(x==1)
        return 0;
    for(int i=2; i*i<x; i++)
    {
        if(x%i==0)
            return 0;
    }
    return 1;
}
long long mod=1000000007;
long long pow_(long long base, long long exponent, int modulus)
{
    long long result = 1;
    while (exponent > 0)
    {
        if (exponent % 2 == 1)
            result = (result * base) % mod;
        exponent = exponent >> 1;
        base = (base * base) % mod;
    }
    return result;
}
int main()
{
    ios::sync_with_stdio(0);
    cin.tie(0);
    cout.tie(0);
    /*********************/
    int n,k;double sum;
    cin>>n>>k;
    double arr[1000];
    for(int i=0;i<n;i++)
        {
            cin>>arr[i];
            sum+=arr[i];
        }
    long long mn=1e9;
    for(int i=1;i<=k;i++)
    {
        long long j=0;
        for(j;j<=10000;j++)
        {
            double a=(sum+i*j)/(j+n);
            long long b=(long long)round(a);
            if(b>=k)
            {
                mn=min(j,mn);
                break;
            }
        }
    }
    cout<<mn<<endl;
  return 0;
}

#include <bits/stdc++.h>
#define sf scanf
#define pf printf
#define REP(i,n) for (int (i)=0; (i)<(n); (i)++)
#define REPS(i,s,n) for (int (i)=(s); (i)<=(n); (i)++)
using namespace std;
inline string GetString(void){
  char x[1000005];
  scanf("%s",x); string s = x;
  return s;
}

int main()
{
    int n, k;
    sf("%d %d",&n, &k);
    int div=0;
    int total=0;
    int ans=0;
    float now=0;
    REP(i,n){
        int num;
        sf("%d",&num);
        div++; total+=num;
        now=(float)total/div;
        if (now>=(float)k-0.5) break;
    }
    while(now < (float)k-0.5)
    {
        total+=k;
        div++;
        ans++;
        now=(float)total/div;
    }
    printf("%d\n",ans);
    return 0;
}

#include <iostream>
#include <cmath>
using namespace std;

int main()
{ float numofgrad,mixgrade,grade;
cin>>numofgrad>>mixgrade;
float a=numofgrad;
float av=0,sum=0;
for (int i=0;i<numofgrad;i++){
cin>>grade;
sum+=grade;
av=ceil(sum/a);
if (av==mixgrade){
cout<<a-numofgrad;
break;
}
else {
a++;
av=ceil(sum+mixgrade)/a;
}
}
cout <<a;

    return 0;

}

#include<bits/stdc++.h>
using namespace std;

int main(){

    float n,k,sum=0,temp;
    cin>>n>>k;
    for(int i=0;i<n;++i){
        cin>>temp;
        sum+=temp;
    }
    cout<<endl<<endl<<sum/n<<endl<<endl;
    if(sum/n >=(k-0.5)){
        cout<<0;
    }
    else{
        int m=(n*(k-0.5) - sum)/0.5;
        cout<<m;
    }

    return 0;
}

#include <bits/stdc++.h>
#define mp make_pair
using namespace std;
typedef pair<int, int> pii;

int n, k, m;
long long ans, tmp;
int main() {
	ios::sync_with_stdio(false), cin.tie(0), cout.tie(0);
	cin>> n >> k;
	ans = 0;
	m = 0;
	for(int i = 0; i < n; i++) {
		cin>> tmp;
		ans += tmp;
	}
	int l = 0; int r = 1000;
	while(l <= r) {
		m = (l + r)/2;
		double tt = (double)(ans + m*k)/(n + m);
		if(tt < k - 0.5)
			l = m + 1;
		else
			r = m - 1;
	}
	if((double)(ans + m*k)/(n + m) < (k - 0.5)) m++;
	if((double)(ans + (m - 1)*k)/(n + m - 1) > (k - 0.5)) m--;
	cout<< m << endl;
	return 0;
}

#include<iostream>
using namespace std;
int main()
{
    double k;
    int n;
    cin >> n >> k;
    double a[n],t=0,h=0,o=0;
    for(int i=0; i<n; i++)
    {
        cin >> a[i];
        t=t+a[i];
    }
    if(t/n >= k-0.5)
        cout << 0;
    else{
    for(long long int i=0; i<10000000; i++)
    {
        h=(t+(i+1)*k)/(n+i+1);
        if(h==(k-0.5))
            break;
        else
            o++;
    }
    }
    cout << o+1;
}

#include<iostream>
using namespace std;
int main()
{
    long long n,k;
    cin>>n>>k;
    long long a[n];
    for(int i=0;i<n;i++)
        cin>>a[i];
    long long t=0;
    for(int i=0;i<n;i++)
        t+=a[i];
    if(t/n==1||((t/n)>=(2*k-1)/2))
        cout<<"0";
    else
    {
    long long z;
    z=2*n*k-n-2*t;
    cout<<z;
    }

    return 0;
}

#include <stdio.h>
#include <conio.h>
#include <iostream>

using namespace std;

int main()
{
	int arr[100];
	int size, max;
	cin >> size >> max;
	int quantity = size;
	int answer=0;
	double notes = 0;
	double need_note = max - 0.5;
	double buff = 0;
	for (int i = 0; i < size; i++)
	{
		cin >> arr[i];
		notes += arr[i];
	}

	while (buff < need_note)
	{
		size++;
		notes += max;
		buff =  notes / size;
		answer++;
	}

	cout << answer << endl;
	return 0;
}

#include<bits/stdc++.h>
using namespace std;
int main()
{
    int n,x,a,c,p,y,q,s=0;

    cin>>n>>x;

    while(n--)
       { cin>>a;
          p=(x-a);
          s+=p;
       }
       cout<<s;

}

#include <iostream>
#include <cmath>

using namespace std;

int main()
{
    int n, k, sum = 0;
    cin >> n >> k;
    for(int i = 0; i < n; ++i)
    {
        int x;
        cin >> x;
        sum += x;
    }
    int le = 0, ri = 1e7;
    while(ri - le > 1)
    {
        int m = (ri + le) / 2;
        if(round(double(sum + m * k) / (n + m)) < k)
            le = m;
        else
            ri = m;
    }
    cout << ri << endl;
    return 0;
}

#include <bits/stdc++.h>

using namespace std;

int main()
{
	int n, k;
	cin >> n >> k;
	double p = 0.0, EPS, c, mx = 0.0;
	for(int i = 0; i < n; i++)
	{
		cin >> p;
		c += p;
		mx = max(mx, p);
	}
	int j = 0;
	while(((c / (n + j)) + 0.5) < k)
	{
		c += p + 1;
		j++;
	}
	cout << j << '\n';

	return 0;
}

#include <bits/stdc++.h>
using namespace std;
int main()
{
    int n,k,i;
    double sum=0,num,av;
    cin>>n>>k;
    int a[n];
    for(i=0;i<n;i++)
    {
        cin>>a[i];
        sum=sum+a[i];
    }
    for(i=1;;i++)
    {
        sum=sum+k;
        num=n+i;
        av=sum/num;
        if(av>=(k-0.5))
        {
            cout<<i<<endl;
            return 0;
        }
    }
    return 0;
}

#include <iostream>

using namespace std;

int notas[1000];

int main()
{
    int n,k,sum,coc; cin >> n >> k; sum = 0;
    long long w;
    double res;

    for (int i = 0; i < n; i++)
    {
        cin >> notas[i];
        sum += notas[i];
    }
    res = sum%n;
    coc = sum/n;

    if ((res >= 0.5 && coc == k-1)||(res == 0 && coc == k))
    {
        cout << 0;
    }
    else
    {
        w = 2*((k*n)-sum-(0.5*n));
        cout << w;
    }
}

#include <bits/stdc++.h>
using namespace std;

int main(){
	long long n,k;
	cin >> n >> k;
	long long mark[n];
	long long sum = 0;
	for(long long i=0;i<n;i++){
		cin >> mark[i];
		sum += mark[i];
	}
	for(long long i=1;;i++){
		long long new_sum = sum + i*k;

		if((k*(n+i)-new_sum)*2 <= (n+i)){
			cout << i << endl;
			break;
		}
	}
	return 0;
}

#include <bits/stdc++.h>
#include <iostream>

//freopen("input.txt", "r", stdin);
//freopen("output.txt", "w", stdout);

using namespace std;

// © ℙ𝕖𝕥𝕖𝕣 𝕄𝕪𝕙𝕒𝕝𝕖𝕙𝕒

int main() {
    int n,k;
    cin >> n >> k;
    double sum = 0;
    for(int i = 0; i<n; i++){
        int x; cin >> x;
        sum+=x;
    }

    if(round(sum/n) >= k)return cout <<0,0;

    for(int i = 1; i<=10000; i++){
        sum+=k;
        ++n;
        if(round(sum/n) >=k)return cout << i,0;
    }
}

#include <iostream>
using namespace std;

int verif(int s, int nrnote)
{
    float ma = 0;
    int finall = 0;

    ma = (float)s / nrnote;

    if(ma - (int)ma < 0.5)
        finall = (int)ma;
    else
        finall = (int)ma + 1;

    return finall;

}
int main()
{
    int n, k, i, s = 0, nota, nr_note = 0, finall;
    float ma = 0;

    cin >> n >> k;

    for(i = 0; i < n; i++)
    {
        cin >> nota;

        s = s + nota;
        nr_note++;
    }

    int nr = 1, final1;

    final1 = verif(s, nr_note);

    if(final1 == k)
        cout << 0;
    else
        while(final1 != k && nr <= k)
        {
            int s1 = s, nr_note1 = nr_note, j = 0;
            float ma1 = ma;

            for(i = k; i > 0 && j < nr; i--)
            {
                s1 = s1 + k;
                nr_note1++;
                j++;
            }

            final1 = verif(s1, nr_note1);

            if(final1 == k)
            {
                cout << nr;
                break;
            }

            nr++;
        }

    return 0;
}

#include<bits/stdc++.h>
using namespace std;

int main(){

    int n,k,sum=0,temp;
    cin>>n>>k;
    for(int i=0;i<n;++i){
        cin>>temp;
        sum+=temp;
    }
    if(sum/n == k){
        cout<<0;
    }
    else{
        int m=(n*(k-0.5) - sum)/0.5;
        cout<<m;
    }

    return 0;
}

#pragma warning(disable:4996)
#include<iostream>
#include<cstdio>
#include<algorithm>
#include<vector>
#include<cstring>
#include<stdio.h>
typedef long long ll;
using namespace std;
int ro(double x) {
	return x > (int)x ? (int)x + 1 : (int)x;
}
int main()
{
	double n, k, a;
	scanf("%d%d", &n, &k);
	double ans = 0;
	for (int i = 0; i < n; i++) {
		scanf("%d", &a);
		ans -= 2*a;
	}
	ans += n*(2 * k - 1);
	printf("%d\n", (int)ans);
	return 0;
}

#include <cstdio>
#include <cmath>
using namespace std;

int main()
{
	float Promedio;
	int Marcas, Maximo, MarcasNora;
	scanf("%d %d", &Marcas, &Maximo);
	for (int i=0; i<Marcas; i++){
		scanf("%d", &MarcasNora);
		Promedio+= MarcasNora;
	}
	//Promedio/= Marcas;
	int cont = 0;
	while( (float)(Promedio/(Marcas+cont)) < (float)(Maximo-0.5) ){
		//printf("%f - %f\n", (Promedio/(Marcas+cont)), round(Promedio/(Marcas+cont)));
		cont++;
		Promedio+= Maximo;
	}
	printf("%d", cont);
	return 0;
}

#include<bits/stdc++.h>

using namespace std;

int main() {

	int n, k, c, ans = 0;

	cin >> n >> k;

	for( int i = 0; i < n; i ++ ) {

		scanf("%d", &c);

		ans += ( k - c ) * 2 - 1;

	}

	cout << ans << endl;

	return 0;

}

#include <bits/stdc++.h>
using namespace std;
long long GCD(long long  n1, long long n2)
{
    if (n2 != 0)
        return GCD(n2, n1 % n2);
    else
        return n1;
}
long long LCM(long long  n1, long long n2)
{
    long long m;
    m=n1*n2/GCD(n1,n2);
    return m;
}
unsigned long long choose(unsigned long long n, unsigned long long k)
{
    if (k > n)
    {
        return 0;
    }
    unsigned long long r = 1;
    for (unsigned long long d = 1; d <= k; ++d)
    {
        r *= n--;
        r /= d;
    }
    return r;
}
bool isprime(int x)
{
    if(x==1)
        return 0;
    for(int i=2; i*i<x; i++)
    {
        if(x%i==0)
            return 0;
    }
    return 1;
}
long long mod=1000000007;
long long pow_(long long base, long long exponent, int modulus)
{
    long long result = 1;
    while (exponent > 0)
    {
        if (exponent % 2 == 1)
            result = (result * base) % mod;
        exponent = exponent >> 1;
        base = (base * base) % mod;
    }
    return result;
}
int main()
{
    ios::sync_with_stdio(0);
    cin.tie(0);
    cout.tie(0);
    /*********************/
    int n,k;double sum;
    cin>>n>>k;
    double arr[1000];
    for(int i=0;i<n;i++)
        {
            cin>>arr[i];
            sum+=arr[i];
        }
    long long mn=1e9;
    for(int i=1;i<=k;i++)
    {
        long long j=0;
        for(j;j<=10000;j++)
        {
            double a=(sum+i*j)/(j+n);
            long long b=(long long)round(a);
            if(b>=k)
            {
                mn=min(j,mn);
                break;
            }
        }
    }
    cout<<mn<<endl;
    long long m=sum/n;
    cout<<m<<endl;
    cout<<2*n*k-2*sum-n<<endl;
  return 0;
}

#include<iostream>
#include<cmath>
#include<stdio.h>
using namespace std;

int roundoff(double k){
	if(k-floor(k)<0.5){
		return floor(k);
	}
	else
		return ceil(k);
}

int main(){
	int n,k;
	int marks[101];
	double sum=0;
	cin>>n>>k;
	for(int i=0;i<n;i++){
		cin>>marks[i];
		sum+=marks[i];
	}
	int count=0;
	double avg=sum/n;
while(roundoff(avg)<k){
	count++;
	avg=((avg*n)+k)/(n+1);
	n++;
}
cout<<count<<endl;
	return 0;
}

#include <bits/stdc++.h>

using namespace std;

double gerd (double a) {
	double g;
	while (g < a) {
		g++;
	}
	if (g - a > 0.5) {
		g -= 1;
	}
	return g;
}

double n, k, m, s, ans, av;

int main () {
	cin >> n >> k;
	for (int i = 0; i < n; i++) {
		cin >> m;
		s += m;
	}
	av = s / n;
	if (gerd (av) == k) {
		cout << 0;
		return 0;
	}
	while (gerd (av) < k) {
		s += k;
		ans++;
		av = s / (n + ans);
	}
	cout << (int) ans;
	return 0;
}

#include <bits/stdc++.h>
typedef long long int ll;
using namespace std;

ll a[102];
int main()
{
    double n,k;
    cin>>n>>k;
    double sum=0;
    double ans=0;
    for(int i=0;i<n;i++)
    {
        cin>>a[i];
        sum+=a[i];
    }
    ans=2*(double)(n*k-(double)n/2-sum);
    cout<<ans<<endl;
    return 0;
}

#include <iostream>

using namespace std;

int main()
{
    float n,i,m,s=0,j;
    float p=0,k;
    cin>>n>>k;
    for(i=0;i<n;i++)
    {
        cin>>m;
        s=s+m;
    }

    j=-2*s-n+2*k*n;
    cout<<j;

        return 0;
}

#include <cstdlib>
#include <iostream>
#include <string>
#include <string.h>
#include <math.h>
#include <map>
#include <vector>
#include <set>
#include <queue>
#include <algorithm>
#include <functional>
#include <iomanip>
#include <stdio.h>
#include <stdlib.h>
#include <memory.h>
#include <complex>
using namespace std;
typedef long long         ll;
ll modulo(ll m , ll n){
    return m >= 0 ? m%n : (n-abs(m%n))% n ;
}
int main() {
   ll n , k ,y;
    cin>>n>>k;
  float sum=0 ;
    for(int i =0 ; i <n ; i++){
        cin >> y;
        sum+=y;
    }
if( round ( sum/n ) +0.5 >= (k) ) {
            cout << 0 ;
            return 0;
        }
    for(int i =1 ; i <=10000 ; i++){
        sum+=k ;

        if( ( round( sum/(n+i) ) +0.5)   >= k ) {
            cout<< i ;
            return 0;
        }
    }

}

#include<bits/stdc++.h>
using namespace std;
int main()
{
    float sum,p=0,n;
    int a,b,i,j,k;
    cin>>a>>b;
    p=(float)(b+(b-1))/2;
    for(i=0;i<a;i++)
    {
        cin>>k;
        sum+=k;
    }
    n=sum/a;
    i=0;cout<<n;
    while(n<p)
    {
        sum+=b;a+=1;i++;
        n=sum/a;
    }cout<<i;
}

#include<bits/stdc++.h>
using namespace std;
#define MP         make_pair
#define PB         push_back
#define LL         long long
#define MAX        1000005
#define mod        1000000007
#define debug(a)   cout<<a<<"\n"
#define mx(a,b,c)  max(a,max(b,c))
#define mn(a,b,c)  min(a,min(b,c))
#define pred(a)    printf("%0.6lf",a);
#define rep(i,x,b) for(int i=x;i<b;i++)
#define fast()     ios_base::sync_with_stdio(0)
const double eps=1e-9;
const double pi =acos(-1);
struct sx{};
bool cmp(){}
LL t1,t2,t3,t4,t5,t6;
bool c;
int main()
{

fast();
double n,k,x,a,d1;
cin>>n>>k;
rep(i,0,n)
{
  cin>>a;
  d1+=a;

}

x=(n*1.0*(2.0*k-1.0)-2.0*d1);
x=(LL)x;
cout<<x;
}

#include <stdio.h>
#include <iostream>
#include <queue>
#include <string>
#include <algorithm>
#include <cstdio>
#include <stack>
#include <vector>
#include <map>
#include <ctime>
#include <cmath>
#include <string.h>
#define inf 0x7fffffff
using namespace std;
struct I
{
    int x,y;
};

int a,b,c,k,n,m,i,e,d,o[100010],l[200212],dx[20]={1,0,-1,0},dy[20]={0,1,0,-1},dz[20]={1,-1};
long long x,y,z[110];
//map <string,int> m;
I j[3][501060];

stack<int> s;
//char r[55];
//deque<int> d;
struct P
{
    int x,y,z;
    bool operator<(const P &a)const
    {

            return x>a.x;

    }
};
double u;
//P u[500000];
vector <int> v[211010];
queue<int> q;
string r,r1[100];
map<int,int > p;
//A==65
//Z==90

//a==97

int main()
{
    double b,c,d;
    scanf("%d %lf",&a,&b);
    for(int t=1;t<=a;c+=d,t++)
        scanf("%lf",&d);
    for(int t=a;;t++)
    {
        if((b-0.5)*(double)t<=c)
        {
            puts("1");
            //printf("%d",t-a);
            return 0;
        }
        c+=b;
    }
}

#include <iostream>
#include <cmath>
//#include <vector>
using namespace std;

#define ll long long
#define ar array

int main() {
    ios::sync_with_stdio(0);
    cin.tie(0);
    int n, k;
    cin >> n >> k;
    int sum = 0;
    for (int i = 0; i < n; i++)
    {
        int a;
        cin >> a;
        sum += a;
    }
    int av = round(sum / n);
    int i = 1;
    while (av < k)
    {
        sum += k;
        av = round((double) sum / (n + i));
        i++;
    }
    cout << i - 1 << "\n";
    return 0;
}

#include <iostream>

using namespace std;

int main() {
  int N, K;
  std::cin >> N >> K;
  int64_t num = 0;
  int64_t den = N;
  for (int i = 0; i < N; ++i) {
    int64_t x;
    cin >> x;
    num += x;
  }
  for (int j = 0; j < 10000; ++j) {
    int64_t DEN = den + j;
    int64_t NUM = num + j * K;
    if (NUM / DEN < K - 1) continue;
    int64_t lhs = NUM;
    int64_t rhs = K * DEN;
    if (lhs >= rhs || 2 * (NUM % DEN) >= DEN) {
      cout << j << endl;
      return 0;
    }
  }
  cout << -1 << endl;
}

#include <bits/stdc++.h>

using namespace std;

int main()
{
    int a,b,i,c;
    double sum=0,av;
    cin>>a>>b;
    for (i=0;i<a;i++)
    {
        cin>>c;
        sum=sum+c;
    }
    for (i=1;i<10;i++)
    {
        sum=(sum+b);
        av=sum/(a+i);
      // cout<<av<<" "<<a+i<<endl;;
        if (round(av)==b) {
            cout<<i;
            break;
        }
    }
}

//freopen("input.txt","r",stdin);
//   freopen("output.txt","w",stdout);
#include <bits/stdc++.h>
using namespace std;
#define op                            \
    ios_base::sync_with_stdio(false); \
    cin.tie(0);                       \
    cout.tie(0)
#define pi 3.1415926536
int main()
{
    op;
    int m;
    double n,sum1=0,sum2=0;
    cin>>m>>n;

    int i,x,a[m],d=0,z;
    z=n;
    for(i=0;i<m;i++)
      {
          cin>>a[i];
          sum1+=a[i];

      }
    sum2=sum1;
    n=n-0.5;
    while(1)
    {
        sum1+=z;
        m++;
        d++;
        if(sum1/m >= n && sum1/m <= n+0.5)
           {
              cout<<d<<endl;
              return 0;
           }
    }
}