#include <stdio.h>
#include <stdlib.h>
#include <math.h>
#include <string.h>

int main () {

	int a, b;
	int h1, h2;
	int i = 0;
	int j = 14;

	scanf("%d %d", &h1, &h2);
	scanf("%d %d", &a, &b);
// printf("%d %d\n", h1, h2);
// printf("%d %d\n", a, b);
	if (h1 + 8 * a >= h2) { //alcanca no 1 dia
		printf("0\n");
		return 0;
	}
	if (a <= b) {
		printf("-1\n");
		return 0;
	}
// 	printf("#\n");
	while (1) {
// 		printf("%d %d\n", h1, h2);

		if (10 <= j && j < 22) { //dia
			h1 += a * (22 - j);

			if (h1 >= h2) {
// 				if (h1 - 8 * a >= h2)
// 					i--;
				printf("%d\n", i);
				break;
			}
			i++;
			j = 22;
		} else { //noite
			h1 -= b * (j - 10);
			j = 10;
		}
	}

	return 0;

}

# include <stdio.h>

int main ()
{
    int a,b,u,v;
    scanf("%d %d %d %d",&a,&b,&u,&v);
    int x=b-a;
    int z=12*v;
    int y=8*u;
    int w=12*u;
    if(x<=(8*u)) {printf("0"); return 0;}
    if(x>(8*u) && u<v) {printf("-1"); return 0;}
    //if(a+y-z < 0) {printf("1"); return 0;}
    else a=a+y-z;
    //if(a+y<0) printf("1") return 0;
    for(long int i=1;i<100005;i++){
        if(a+w>=b)
            {printf("%ld",i);
                return 0;}
        else a=a+w-z;
         continue;
    }
    printf("-1");
    return 0;
}

#include<stdio.h>
int main()
{
    int a,b,c,d,x,y,i,j,cnt=0,flag;

    scanf("%d%d%d%d",&a,&b,&c,&d);
    if(d>=c&&(b-a-8*c)>0)
       flag=0;
    else
    flag=1;
   if(flag==1) {j=(b-a-8*c);
   i=0;
    while(1)
    {
       if(j<=0)
       {
           break;
       }
       cnt++;
       j=j+12*d;
       j=j-(12*c);

    }
    printf("%d",cnt);}

if(flag==0)
    printf("-1");

    }

#include <stdio.h>
#include <string.h>
#include <stdbool.h>

#define clr(ar) memset(ar, 0, sizeof(ar))
#define read() freopen("lol.txt", "r", stdin)

int main(){
    long long i, j, k, l, x, h1, h2, a, b;

    while (scanf("%lld %lld %lld %lld", &h1, &h2, &a, &b) != EOF){
        long long hour = 14, days = 0, lim = 1e8;

        while (h1 < h2 && lim--){
            if (hour >= 10 && hour < 22) h1 += a;
            else h1 -= b;
            hour++;
            if (hour == 24) hour = 0;
            if (hour == 10) days++;
        }

        if (lim <= 0) days = -1;
        printf("%lld\n", days);
    }
    return 0;
}

#include<stdio.h>
#include<string.h>
int main()
{
	int s,e;
	int u,d;
	int len;
	int day=0,flag=1;
	scanf("%d %d",&s,&e);
	scanf("%d %d",&u,&d);
	len=e-s;
	if(u*8>=len) printf("0\n");
	else if(u<=d) printf("-1\n");
	else
	{
		day=0;flag=1;
		len=len-u*8;
		while(flag==1)
		{
			len+=12*d;
			len-=12*u;
			day++;
			if(len<=0) flag=0;
		}
		printf("%d\n",day);
	}
}

#include <stdio.h>

/*
 * http://codeforces.com/problemset/problem/652/A
 */
int main()
{
    int hc = 0, ha = 0;
    scanf("%d %d", &hc, &ha);

    int a = 0, b = 0, d = 0;
    scanf("%d %d", &a, &b);

    hc += 8 * a;

    if (hc < ha && a <= b) {
        printf("-1\n");

        return 0;
    }

    while (hc < ha) {
        hc += a * 12 - b * 12;
        d += 1;
    }

    printf("%d\n", d);

    return 0;
}

#include<stdio.h>
#include<stdbool.h>

int main(){
    long long int h1,h2,a,b;
     scanf("%lld %lld",&h1,&h2);
     scanf("%lld %lld",&a,&b);
     int i;
     long long int dist=h1;
     bool day=1,first=1,sec=1;
     long long int count=0;
     if(b>=a&&(h2-h1)>(8*a))
      printf("-1");
      else{
      while(1){
           if(dist>=h2)
            break;
           if(day&&first){
            dist+=(a*8);
            day=0;
            first=0;
           }
           else if(!day){
            dist-=(b*12);
            count++;
            day=1;
           }
           else if(!first){
               dist+=(a*12);
               day=0;
               sec=0;
           }

      }
      }
      if(dist>=h2)
      printf("%lld",count);

}

#include<stdio.h>
int main()
{
    int h1,h2,a,b,d1,s,p,count=0;
    scanf("%d%d",&h1,&h2);
    scanf("%d%d",&a,&b);

    d1=a*8;

    s=h1+d1;
    if(h1+d1<h2)
    {
        if(a<=b)
        {
            printf("-1");
        }
        else
        {
        while(1)
        {

            if(s>=h2)
            {
                printf("%d",count);
                break;
            }
            else
            {
                s=s-(b*12);
                s=s+(a*12);
                count++;

            }
        }
        }
    }
    else
    {
        printf("0");
    }
    return 0;
}

#include <stdio.h>
#include <stdlib.h>
#include <math.h>

int main()
{
    long long h1,h2,a,b,h,step,days;

    scanf("%lld %lld",&h1,&h2);
    scanf("%lld %lld",&a,&b);

    if(b>=a && (8*a)<(h2-h1))
        printf("-1");

    else if(8*a >= h2-h1)
        printf("0");

    else
    {
        h = h2 - (h1 + 8*a);
        step = 12*(a-b);
        days = ceil((double)h/step);
        printf("%lld",days);
    }

    return 0;
}

#include<stdio.h>
int main(){
    int a,b,c,d,e,f,g;
    int first,second;
    int up,down;
    scanf("%d%d",&first,&second);
    scanf("%d%d",&up,&down);
    if(((first + 8*up) - (12 * down) + 4*up) <= first && (((8*up)+first) < second)){
    printf("-1");
    return 0;}
    if(up == down && (((8*up)+first) < second)){
    printf("-1");
    return 0;
    }
    int cnt=0,i;
    if(first>=second){
    printf("0");
    return 0;}
    while(1){
    for(i=0;i<8;i++){
    first+=up;
    if(first>=second){
    printf("%d",cnt);
    return 0;
    }}
    for(i=0;i<12;i++){
    first-=down;
    if(first>=second){
    printf("%d",cnt);
    return 0;
    }}
    cnt++;
    for(i=0;i<4;i++){
    first+=up;
    if(first>=second){
    printf("%d",cnt);
    return 0;
    }}
    }
}

#include<stdio.h>
int main()
{
	int h1,h2,a,b,diff=0,height=0,day,val=0;
	scanf("%d%d",&h1,&h2);
	scanf("%d%d",&a,&b);
	diff = h2-h1;
	height= diff-8*a+12*b;
	day=0;
	val=val+12*b-12*a;
	if (8*a<diff&&b>=a)
		day=-1;
	else if (8*a>diff)
		day=0;
	else
	{
		while (height>12*b)
		{
			height+=val;
			day=day+1;
		}
	}
	printf("%d",day);
	return 0;
}

#include <stdio.h>
#include <stdlib.h>

int h1,h2,a,b,nr;

int main()
{
   scanf("%d %d %d %d",&h1,&h2,&a,&b);
  h1=h1+a*8;
   if(h1>=h2)
    printf("0");
   else
    if(a<=b)
        printf("-1");
   while(h1<h2 && a>b)
   {
       h1=h1-12*b;
       h1=h1+12*a;
       nr++;

       if(h1>=h2)
    printf("%d",nr);
   }

    return 0;
}

#include<stdio.h>
typedef unsigned u;
int h1,h2;
int main()
{
	u t=0,c=10,a,b;
	scanf("%i%i%u%u",&h1,&h2,&a,&b);
	for(h1-=4*a;h1<h2;++c)
	{
		if(c==24){c=0;++t;if(a<=b){t=-1;break;}}
		if(c>9&&c<22)h1+=a;
		else h1-=b;
	}
	printf("%i\n",t);
	return 0;
}

#include<stdio.h>
int main()
{
    int n,m,a,b,i,j;
    scanf("%d %d %d %d",&n,&m,&a,&b);
    if(a<=b)
    {
        if(a*8>=(m-n))
            printf("0\n");
        else
            printf("-1\n");
    }

    else
    {
        i=0;
        while(1)
        {
            n+=8*a;
            if(n>=m)
            {
                printf("%d\n",i);
                break;
            }
            i++;
            n-=12*b;
            n+=4*a;
            if(n>=m)
            {
                printf("%d\n",i);
                break;
            }

        }
    }

    return 0;
}

#include <stdio.h>

int main()
{
  int h1, h2, a, b, ans = 0;
  scanf("%d %d", &h1, &h2);
  scanf("%d %d", &a, &b);

  if (a <= b && h2 - h1 - a * 8 > 0) {
    printf("-1\n");
    return 0;
  }

  int dis = h2 - h1 - a * 8;
  if (dis <= 0) {
    printf("0\n");
    return 0;
  }
  ans += 1;

  while (dis > 0) {
    dis -= (a - b) * 12;
    if (dis <= 0) break;
    ans+= 1;
  }

  printf("%d\n", ans);
  return 0;
}

#include<stdio.h>

int main()
{
    int i , ha , hc , a , b ;

    scanf("%d%d%d%d",&hc,&ha,&a,&b) ;

    if((b>a && 8*a < ha-hc) || (b==a && 12*a < ha-hc+12*b-8*a))
    {
        printf("-1");
        return 0 ;
    }

    for(i=0 ; ; i++)
    {
        if(!i)hc += a*8;
        else hc += a*12 ;

        if(hc >= ha)
        {
            printf("%d",i);
            return 0 ;
        }
        hc -= b*12 ;
    }

    return 0 ;
}

#include <stdio.h>

int main()
{
    int h1,h2,a,b,day=0,h,p=0;
    scanf("%d %d %d %d",&h1,&h2,&a,&b);
    h=h1+a*8;
    if(h>=h2)
        printf("0");
    else
    {
        while(h<h2)
        {
            h=h-12*b+12*a;
            day+=1;
            if(b>=a && day>1)
            {
                printf("-1");
                p=1;
                break;
            }
        }
        if(p!=1)
            printf("%d",day);
    }
    return 0;
}

#include <stdio.h>

int main()
{
	int h1, h2, up = 0, down = 0;

	fscanf(stdin, "%d %d %d %d", &h1, &h2, &up, &down);

	int days = 0;
	int currentHour = 14;
	int flag = 0;

	while (1)
	{

		if ((currentHour >= 10)  && (currentHour < 22))
		{
			h1 += up;
			currentHour++;
			if (h1 >= h2)
			{
				break;
			}
		}
		else
		{
			if (currentHour == 23)
			{
				currentHour = 0;
				flag = 1;
				days++;
			}
			else
			{
				currentHour++;
			}
			h1 -= down;
		}

		if ((down >= up) && (flag == 1))
		{
			days = -1;
			break;
		}
	}

	printf("%d", days);

}

#include<stdio.h>

int cat(int a,int b,int h1, int h2,int d,int v,int z)
{   int pos=0,k=0,nh;
    if((z==h1) && (d>0))
    {
        k=-1;
	printf("%d",k);
	return 0;
    }
       pos=(a*8)+h1;
    if(pos>=h2)
    {
        k=d;
        printf("%d",k);
        return 0;
    }
    d++;
    pos-=(b*12);
    pos=pos+a*4;
    nh=pos;
    if(v>pos && d>2)
    {
        d=-1;
	printf("%d",d);
	return 0;
    }
     if(pos>=h2)
    {
        k=d;
        printf("%d",k);
        return 0;
    }
    cat(a,b,nh,h2,d,pos,z);
}

int main()
{
    int a,b,h1,h2,d=0,v=0;
    scanf("%d%d",&h1,&h2);
    scanf("%d%d",&a,&b);

cat(a,b,h1,h2,d,v,h1);
return 0;
}

// Gabriel and Caterpillar

#include<stdio.h>
int main(void)
{
	int h1,h2,x,a,b,i,count,flag;
	scanf("%d %d",&h1,&h2);
	scanf("%d %d",&a,&b);
	if(h1<h2)
	{
		x = h1 - 4*a;
		count = 0;
		for(i = 0;;i++)
		{
			count+=1;
			x = x+12*a;
			if(x>=h2)
			{
				flag = 1;
				break;
			}
			x = x-12*b;
			if(x<=(h1-4*a))
			{
				flag = 0;
				break;
			}
		}
		if(flag==0)
			printf("-1\n");
		else if(flag==1)
			printf("%d\n",count-1);
	}
	return 0;
}

#include <stdio.h>

#define S_N 8
#define DN 12
#define D_S 4

int main() {

    int h1, h2;
    int a, b;

    scanf("%d%d", &h1, &h2);
    scanf("%d%d", &a, &b);

    h1 += S_N * a;
    if (h1 >= h2) {
        printf("0");
        return 0;
    }
    if (a <= b) {
        printf("-1");
        return 0;
    }
    if ((h2 - h1) % ((a - b) * DN))
        printf("%d", (h2 - h1) / ((a - b) * DN) + 1);
    else
        printf("%d", (h2 - h1) / ((a - b) * DN));
    return 0;

}

#include<stdio.h>
int main()
{
    int h1,h2,a,b;
    scanf("%d%d%d%d",&h1,&h2,&a,&b);
    if(a<=b && h1+8*a<h2)
    {
        printf("-1\n");
        return 0;
    }
    int ans=0;
    while(1)
    {
        h1=h1+8*a;
        if(h1>=h2)
        {
            break;
        }
        h1=h1-b*12;
        ans++;
        h1=h1+4*a;
    }
    printf("%d\n",ans);
    return 0;
}

#include <stdio.h>
int main()
{
    int h1, h2, a, b, day = 0;
    scanf("%d%d%d%d", &h1, &h2, &a, &b);
    h1 += a*8;
    if( h1>=h2 )
    printf("0\n");
    else
    {
       day++;
       while(1)
       {
           h1 -= b*12;
h1 += a*12;
 if( h1>=h2 )
{
 printf("%d\n", day);
 break;
 }
 if( b>=a )
 {
 printf("-1\n");
            break;
        }
        day++;
        }
    }
    return 0;
}

#include<stdio.h>
int main()
{
    long long int x,y,a,b,i,l=0;
    scanf("%lld %lld",&x,&y);
    scanf("%lld %lld",&a,&b);
    if(8*a+x>=y)
    {printf("0");}
    else
    {if(b>=a)
     {printf("-1");}
     else
     {x=x+8*a-12*b;
      i=0;
      while(x<y)
      { i++;
        x=x+(12*a);
        if(x>=y)
        {printf("%lld",i);
         break;
        }
        x=x-12*b;
      }
     }
    }
    return 0;
}

#include<stdio.h>
int main ()
{
	int h1,h2,a,b;
	scanf("%d %d",&h1,&h2);
	scanf("%d %d",&a,&b);
	if(h2-h1<=8*a) printf("%d",0);
	else if(a<=b) printf("%d",-1);
	else{
	h1=h1+a*8-b*12;
	int count=1;
	while(h1+12*a<h2){
		h1=a*12+h1-b*12;
		count++;
	}
	printf("%d",count);}
	return 0;
}

#include <stdio.h>

int main()
{
    int h1, h2, a, b, count=0;
    scanf("%d %d",&h1,&h2);
    scanf("%d %d",&a,&b);
    if(a<=b && a*8<h2-h1) printf("-1\n");
    else
    {
        int temp = 0;
        while(1)
        {
            h1 = h1 + 8*a + temp;
            if(h1>=h2) break;
            else h1 = h1 - 12*b;
            count++;
            temp = 4*a;
        }
        printf("%d\n",count);
    }
    return 0;
}

#include <stdio.h>
#include <stdlib.h>
#include <string.h>
#include <math.h>

#define pi 3.1415926
#define rep(x,ini,end) for(x=(ini);x<(end);x++)
#define per(x,ini,end) for(x=(end-1);x>=(ini);x--)
#define max(x,y) ((x)>(y)?(x):(y))
#define min(x,y) ((x)<(y)?(x):(y))

int main()
{
    int h1, h2;
    scanf("%d %d", &h1, &h2);
    int a, b;
    scanf("%d %d", &a, &b);

    if (h2-h1<a*8)
    {
        printf("0"); return 0;
    }
    if ((h2-h1>a*8) && (a<=b))
    {
        printf("-1"); return 0;
    }

    int day = 0;
    int dayend,nightend;
    while (1)
    {
        if (day == 0)
        {
            dayend = h1 + a * 8;
        }
        else
        {
            dayend = nightend + a * 12;
        }
        if (dayend>=h2)
        {
            printf("%d",day); return 0;
        }
        nightend = dayend - b * 12;
//        if (nightend<=0)
//        {
//            printf("%d",day+1); return 0;
//        }
        day++;
    }

    return 0;
}

#include <stdio.h>

int main(){
    int a,b;
    scanf("%d%d",&a,&b);
    int ai,bi;
    scanf("%d%d",&ai,&bi);
    int k = b - (a + ai * 8);
    if(k <= 0){
        printf("0\n");
    }
    else if(ai <= bi){
        printf("-1\n");
    }
    else{
        printf("%d\n",(k - 1) / ((ai - bi) * 12) + 1);
    }
}

#include<stdio.h>
int main()
{
  long long int a,b,x,y;
  long long int ans=0;
  scanf("%lld%lld",&x,&y);
  scanf("%lld%lld",&a,&b);
  long long int d,d1,d2;
  d=y-x;
  d1=a*8;
  if (d1<d && a<=b) {
    ans=-1;
  }
  else
  {
    d2=d-d1;
    while(d2>0)
    {
      d=d2+b*12;
      d2=d-a*12;
      ans++;

    }
  }
  printf("%lld\n",ans );
  return 0;
}

#include<stdio.h>
int main(){
int a,b,c,d;
scanf("%d%d",&a,&b);
int up,down;
scanf("%d%d",&up,&down);
int minus=((8*up+a)-(12*down))+4*up;
if(minus<=a && ((8*up)+a)<b){
printf("-1");
return 0;
}
int i;
for(i=0;i<8;i++){
a=a+up;
if(a>=b){
printf("%d",0);
return 0;
}}
int cnt=0; int ind=0;
while(1){
if(!ind){
for(i=0;i<12;i++){
a=a-down;
if(a>=b){
printf("%d",cnt);
return 0;
}
}
ind=1;
cnt++;
}
else{
for(i=0;i<12;i++){
a=a+up;
if(a>=b){
printf("%d",cnt);
return 0;
}
}
ind=0;
}
}
}

#include<stdio.h>
int main()
{
	int h1,h2,a,b;
	scanf("%d%d%d%d",&h1,&h2,&a,&b);
	int x=h1+(a*8);int remh;
	if(x>=h2){
		printf("0\n");
		return 0;
	}
	else
		h1=h1+(a*8);
	if(b>=a){
		printf("-1\n");
		return 0;
	}
	long long int day=0;
	while(h1<h2)
	{
		h1=h1+12*(a-b);
		day++;
	}
	printf("%lld\n",day);
	return 0;
}

#include<stdio.h>

int main()
{
    long long int i,h1,h2,a,b,dis,final1;
    scanf("%I64d %I64d",&h1,&h2);
    scanf("%I64d %I64d",&a,&b);
    dis=h1;
    final1=h2;

    i=0;
    while(dis<=h2)
    {
        if(i==0)
        {
            dis=dis+8*a;
        }
        if(i>=1)
            dis=dis+(12*a);
        if(dis>=h2)
            break;
        dis=dis-(2*b);
        if(dis>=h2)
            break;
        i++;
        dis=dis-(10*b);
        if(dis>=h2)
            break;
        if(i>=9000)
        {
            printf("-1");
            return 0;
        }
    }
    printf("%I64d",i);
    return 0;
}

#include <stdio.h>

/*
 * http://codeforces.com/problemset/problem/652/A
 */
int main()
{
    int hc = 0, ha = 0;
    scanf("%d %d", &hc, &ha);

    int a = 0, b = 0, d = 0;
    scanf("%d %d", &a, &b);

    hc += 8 * a;

    if (hc < ha && a <= b) {
        printf("-1\n");

        return 0;
    }

    while (hc < ha) {
        hc += a * 12 - b * 12;
        d += 1;
    }

    printf("%d\n", d);

    return 0;
}

#include<stdio.h>
#define max 100000
int main(){
	long long int a,b,h1,h2,count,flag;
	count=0;
	scanf("%I64d%*c%I64d",&h1,&h2);
	scanf("%I64d%*c%I64d",&a,&b);
	h1=(h1-(4*a));
	flag=0;
	if((h1+(12*a))<h2 && a<=b){
		printf("-1");
		return 0;
	}
	else{
			while(1){
			if((h1+(12*a))>=h2){
				flag=1;
				break;
			}
			else{
				h1=h1+(12*(a-b));
				count++;
			}
		}
	}
	if(flag==1){
		printf("%I64d",count);
	}
	else{
		printf("-1");
	}
	return 0;
}

#include <stdio.h>
#include <stdlib.h>

int
main (int argc, char *argv[])
{
	long int h1,h2,a,b,number=1;
	scanf("%ld %ld",&h1,&h2);
	scanf("%ld %ld",&a,&b);
	int night=12,day=8;
	if (day*a>=h2-h1)
		printf("0\n");
	else if (a<=b)
		printf("-1\n");
	else
	{
		while(a*day+number*(a-b)*night < h2-h1)
			number++;
		printf("%ld \n", number);
	}
	return 0;
}

#include <stdio.h>

int main() {
    int h1, h2, a, b;
    scanf("%d %d", &h1, &h2);
    scanf("%d %d", &a, &b);

    if (h1 + 8 * a >= h2)
        printf("0");
    else if (a <= b)
        printf("-1");
    else {
        int c = h1 + 8 * a - 12 * b, s = 1;
        while (1) {
            int night = c + a * 12;
            if (c <= h2 && h2 <= night) {
                printf("%d", s);
                return 0;
            }
            c = night - 12 * b, s++;
        }
    }
}

#include <stdio.h>

int main(void) {
	long long h1,h2,a,b,k,res;
	scanf("%lld%lld",&h1,&h2);
	scanf("%lld%lld",&a,&b);
	if(a<b)
	{
	    if ((h1+=a*8)<h2)
	    printf("-1");
	    else
	    printf("0");
	}
	if(a==b)
	{
	    if((h1+=a*8)<h2)
	    {
	    printf("-1");
	    }
	    else
	    printf("0");
	}
	if(a>b)
	{
	    k=0;res=0;
	while (h1 < h2)
	{
	    if(k == 0)
		    h1 = h1 + a * 8;
		else
		    h1 = h1 + a * 12;
		k++;
		if (h1 > h2 && (k == 1))
		{
			printf("0");
			return 0;
		}
		if(h1 >= h2)
		{
		    printf("%lld",res);
		    return 0;
		}
		h1 = h1 - 12 * b;
		res++;
	}
		printf("%lld",res);
}

	return 0;
}

#include <stdio.h>

int main()
{
    int h1,h2,a,b;
    while(scanf("%d %d",&h1,&h2)!=EOF)
    {
        scanf("%d %d",&a,&b);
        int c=0,flag=0;
        while(1)
        {
                h1+=8*a;
                if(h1>=h2)
                    break;
                if(a*12<=b*12)
                {
                    flag=1;
                    break;
                }
                h1=h1-12*b+4*a;
                c++;
                if(h1>=h2)
                    break;
        }
        if(flag)
            printf("-1\n");
        else
            printf("%d\n",c);
    }
    return 0;
}

#include <math.h>
#include <stdio.h>
#include <string.h>
#include <stdlib.h>
#include <assert.h>
#include <limits.h>
#include <stdbool.h>

int main(){
    int h1,h2,a,b;
    scanf("%d %d\n%d %d",&h1,&h2,&a,&b);
    h1+=8*a;
    if(h1>=h2)
        printf("0");
    else if(a<=b)
        printf("-1");
    else{
        int diff = h2-h1;
        int mul = 12*(a-b);
        if(diff%mul==0)
            printf("%d",diff/mul);
        else
            printf("%d",diff/mul+1);
    }
    return 0;
}

#include<stdio.h>
int main()
{
    int a,b,c,d,x,y,i,j,cnt=0,flag;

    scanf("%d%d%d%d",&a,&b,&c,&d);
    if(d>=c&&(b-a-8*c)>0)
       flag=0;
    else
    flag=1;
   if(flag==1) {j=(b-a-8*c);
   i=0;
    while(1)
    {
       if(j<=0)
       {
           break;
       }
       cnt++;
       j=j+12*d;
       j=j-(12*c);

    }
    printf("%d",cnt);}

if(flag==0)
    printf("-1");

    }

#include<stdio.h>
int main()
{
	int h1,h2;
	int a,b;
	scanf("%d %d",&h1,&h2);
	scanf("%d %d",&a,&b);
	int no;
	int flag =0;
	int count =0;
	while(1)
	{
		if(count ==0)
			h1 = h1+(8*a);
		else
			h1=h1+(12 * a);
		if(h1 < h2)
			h1=h1-(12 * b);
		if(h1>=h2)
		{
			flag =2;
			break;
		}
		if(b>a ||( (b==a)&&(h1<h2)))
		{
			flag =1;
			break;
		}
		count++;
	}
	if(flag ==1)
		printf("-1");
	else
	{
		printf("%d",count);
	}
	return 0;
}

#include<stdio.h>
#include<math.h>
#include<stdlib.h>
int main()
{
    int a,b,c,d,e,t,r=0,i,p=0,j;
    scanf("%d %d %d %d",&a,&b,&c,&d);

    i=8*c;
    e=b-a;
    t=12*(c-d);
    if(i>=e)
       r=0;
    else if(t<1)
        r=-1;
    else{
        p=i+t;
      for(j=1;;j++){
        if(p>=e){
          r++;
          break;
        }
        else{
            r++;
            p=p+t;
        }

      }

    }

    printf("%d",r);

return 0;
}

#include<stdio.h>
#define MOD 1000000007
typedef long long int llu;
llu mod(llu a) {
	return a>0?a:-1*a;
}
int main()
{
	llu h1,h2,a,b,i,ans=0;
	scanf("%I64d%I64d",&h1,&h2);
	scanf("%I64d%I64d",&a,&b);
	if(b>=a) {
		if( h2>8*a+h1 )
			ans = -1;
		else
			ans = 0;
	}
	else {
		if(h1+8*a>=h2) {
			ans = 0;
		}
		else {
			ans = (h2-(h1+8*a))/(12*(mod(b-a)));
			if((h2-(h1+8*a))%(12*(mod(b-a))))
				ans++;
		}
	}
	printf("%I64d",ans);
	return 0;
}

#include<stdio.h>
int main(){
int n,m,a,b;
while(scanf("%d%d%d%d",&n,&m,&a,&b)!=EOF){
    if(n+8*a>=m) printf("0\n");
        else if(a<=b) printf("-1\n");
        else {
            int i;
            n+=8*a;
            for(i=0;;i++){
               // printf("i=%d,n=%d\n",i,n);
                if(n>=m) break;
                n-=12*b;
                n+=12*a;
            }
            printf("%d\n",i);
        }
    }
return 0;
}

#include <stdio.h>
//#pragma warning (disable : 4996)
int main(int argc, char * argv[])
{
	int a, b; scanf("%d %d", &a, &b);
	int c, d; scanf("%d %d", &c, &d);
	int day = 0;
	a += 8 * c;
	while (1)
	{

		if (a >= b)
		{
			printf("%d", day);
			break;
		}
		if (d >= c)
		{
			printf("-1");
			break;
		}
		day++;
		a += 12 * c - 12 * d;

	}
	return 0;
}

#include <stdio.h>

int main()
{
    int h1, h2, a, b, count=0;
    scanf("%d %d",&h1,&h2);
    scanf("%d %d",&a,&b);
    if(a<b) printf("-1\n");
    else if(a==b) printf("0\n");
    else
    {
        int temp = 0;
        while(1)
        {
            h1 = h1 + 8*a + temp;
            if(h1>=h2) break;
            else h1 = h1 - 12*b;
            count++;
            temp = 4*a;
        }
        printf("%d\n",count);
    }
    return 0;
}

#include <stdio.h>
#include <stdlib.h>
#include <string.h>
#include <math.h>

#define pi 3.1415926
#define rep(x,ini,end) for(x=(ini);x<(end);x++)
#define per(x,ini,end) for(x=(end-1);x>=(ini);x--)
#define max(x,y) ((x)>(y)?(x):(y))
#define min(x,y) ((x)<(y)?(x):(y))

int main()
{
    int h1, h2;
    scanf("%d %d", &h1, &h2);
    int a, b;
    scanf("%d %d", &a, &b);

    if (h2-h1<a*8)
    {
        printf("0"); return 0;
    }
    if ((h2-h1>a*8) && (h2+a*8-b*12>0) && (a<=b))
    {
        printf("-1"); return 0;
    }

    int day = 0;
    int dayend,nightend;
    while (1)
    {
        if (day == 0)
        {
            dayend = h1 + a * 8;
        }
        else
        {
            dayend = nightend + a * 12;
        }
        if (dayend>=h2)
        {
            printf("%d",day); return 0;
        }
        nightend = dayend - b * 12;
//        if (nightend<=0)
//        {
//            printf("%d",day+1); return 0;
//        }
        day++;
    }

    return 0;
}

#include <stdio.h>
#include <stdlib.h>
#include <string.h>
#include <math.h>

#define pi 3.1415926
#define rep(x,ini,end) for(x=(ini);x<(end);x++)
#define per(x,ini,end) for(x=(end-1);x>=(ini);x--)
#define max(x,y) ((x)>(y)?(x):(y))
#define min(x,y) ((x)<(y)?(x):(y))

int main()
{
    int h1, h2;
    scanf("%d %d", &h1, &h2);
    int a, b;
    scanf("%d %d", &a, &b);

    if (h2-h1<a*8)
    {
        printf("0"); return 0;
    }
    if ((h2-h1>a*8) && (h2+a*8-b*12>0) && (a<=b))
    {
        printf("-1"); return 0;
    }

    int day = 0;
    int dayend,nightend;
    while (1)
    {
        if (day == 0)
        {
            dayend = h1 + a * 8;
        }
        else
        {
            dayend = nightend + a * 12;
        }
        if (dayend>=h2)
        {
            printf("%d",day); return 0;
        }
        nightend = dayend - b * 12;
        if (nightend<=0)
        {
            printf("%d",day+1); return 0;
        }
        day++;
    }

    return 0;
}

#include<stdio.h>
int main(){
int a,b,c,d;
scanf("%d%d",&a,&b);
int up,down;
scanf("%d%d",&up,&down);
int minus=((8*up+a)-(12*down))+4*up;
if(minus<=a && ((8*up)+a)<b){
printf("-1");
return 0;
}
int i;
for(i=0;i<8;i++){
a=a+up;
if(a>b){
printf("%d",0);
return 0;
}}
int cnt=0; int ind=0;
while(1){
if(!ind){
for(i=0;i<12;i++){
a=a-down;
if(a>b){
printf("%d",cnt);
return 0;
}
}
ind=1;
cnt++;
}
else{
for(i=0;i<12;i++){
a=a+up;
if(a>b){
printf("%d",cnt);
return 0;
}
}
ind=0;
}
}
}

#include<stdio.h>
int main(){
int a,b,c,d;
scanf("%d%d",&a,&b);
int up,down;
scanf("%d%d",&up,&down);
int minus=((8*up+a)-(12*down))+4*up;
if(minus<0){
    printf("-1");
return 0;
}
if(minus==0 && (8*up)<b){
printf("-1");
return 0;
}
int i;
for(i=0;i<8;i++){
a=a+up;
if(a>b){
printf("%d",0);
return 0;
}
}
int cnt=0; int ind=0;
while(1){
if(!ind){
for(i=0;i<12;i++){
a=a-down;
if(a>b){
printf("%d",cnt);
return 0;
}
}
ind=1;
cnt++;
}
else{
for(i=0;i<12;i++){
a=a+up;
if(a>b){
printf("%d",cnt);
return 0;
}
}
}
}
}

#include<stdio.h>
int main(){
int a,b,c,d;
scanf("%d%d",&a,&b);
int up,down;
scanf("%d%d",&up,&down);
int minus=((8*up+a)-(12*down))+4*up;
if(minus<0){
    printf("-1");
return 0;
}
if(minus==a && ((8*up)+a)<b){
printf("-1");
return 0;
}
int i;
for(i=0;i<8;i++){
a=a+up;
if(a>b){
printf("%d",0);
return 0;
}}
int cnt=0; int ind=0;
while(1){
if(!ind){
for(i=0;i<12;i++){
a=a-down;
if(a>b){
printf("%d",cnt);
return 0;
}
}
ind=1;
cnt++;
}
else{
for(i=0;i<12;i++){
a=a+up;
if(a>b){
printf("%d",cnt);
return 0;
}
}
ind=0;
}
}
}

#include<stdio.h>

int main()
{
    long long int i,h1,h2,a,b,dis,final1;
    scanf("%I64d %I64d",&h1,&h2);
    scanf("%I64d %I64d",&a,&b);
    dis=h1;
    final1=h2;
    if(a<b)
    {
        printf("-1");
        return 0;
    }
    i=0;
    while(1)
    {
        if(i==0)
        {
            dis=dis+8*a;
        }
        else
            dis+=12*a;
        if(dis>=final1)
            break;
        dis-=12*b;
        i++;
    }
    printf("%I64d",i);
    return 0;
}

#include<stdio.h>

int main()
{
    long int i,h1,h2,a,b,dis,final1;
    scanf("%ld %ld",&h1,&h2);
    scanf("%ld %ld",&a,&b);
    dis=h1;
    final1=h2;

    i=0;
    while(dis<=h2)
    {
        if(i==0)
        {
            dis=dis+8*a;
        }
        if(i>=1)
            dis=dis+(12*a);
        if(dis>=h2)
            break;
        dis=dis-(2*b);
        if(dis>=h2)
            break;
        i++;
        dis=dis-(10*b);
        if(dis>=h2)
            break;
        if(i>=10000000)
        {
            printf("-1");
            return 0;
        }
    }
    printf("%ld",i);
    return 0;
}

#include<stdio.h>

int main()
{
    long int i,h1,h2,a,b,dis,final1;
    scanf("%ld %ld",&h1,&h2);
    scanf("%ld %ld",&a,&b);
    dis=h1;
    final1=h2;
    if(a<b&&h2>h1||a<b)
    {
        printf("-1");
        return 0;
    }
    i=0;
    while(dis<=final1)
    {
        if(i==0)
        {
            dis=dis+8*a;
        }
        else
            dis=dis+(12*a);
        if(dis>=final1)
            break;
        dis=dis-(12*b);
        i++;
        if(i>=100000)
        {
            printf("-1");
            return 0;
        }
    }
    printf("%ld",i);
    return 0;
}

#include<stdio.h>

int main()
{
    long int i,h1,h2,a,b,dis,final1;
    scanf("%ld %ld",&h1,&h2);
    scanf("%ld %ld",&a,&b);
    dis=h1;
    final1=h2;

    i=0;
    while(dis<=h2)
    {
        if(i==0)
        {
            dis=dis+8*a;
        }
        if(i>=1)
            dis=dis+(12*a);
        if(dis>=h2)
            break;
        dis=dis-(2*b);
        if(dis>=h2)
            break;
        i++;
        dis=dis-(10*b);
        if(dis>=h2)
            break;
        if(i>=1000)
        {
            printf("-1");
            return 0;
        }
    }
    printf("%ld",i);
    return 0;
}

#include<stdio.h>

int main()
{
    long long int i,h1,h2,a,b,dis,final1;
    scanf("%I64d %I64d",&h1,&h2);
    scanf("%I64d %I64d",&a,&b);
    dis=h1;
    final1=h2;
    if(a<b)
    {
        printf("-1");
        return 0;
    }
    i=0;
    while(1)
    {
        if(i==0)
        {
            dis=dis+8*a;
        }
        else
            dis+=12*a;
        if(dis>=final1)
            break;
        dis-=12*b;
        i++;
        if(i>=100000)
        {
            printf("-1");
            return 0;
        }
    }
    printf("%I64d",i);
    return 0;
}

#include<stdio.h>

int main()
{
    long int i,h1,h2,a,b,dis,final1;
    scanf("%ld %ld",&h1,&h2);
    scanf("%ld %ld",&a,&b);
    dis=h1;
    final1=h2;
    if(a<b&&h2>h1)
    {
        printf("-1");
        return 0;
    }
    i=0;
    while(dis<final1)
    {
        if(i==0)
        {
            dis=dis+8*a;
        }
        else
            dis+=12*a;
        if(dis>=final1)
            break;
        dis-=12*b;
        i++;
        if(i>=100000)
        {
            printf("-1");
            return 0;
        }
    }
    printf("%ld",i);
    return 0;
}

#include<stdio.h>

int main()
{
    long int i,h1,h2,a,b,dis,final1;
    scanf("%ld %ld",&h1,&h2);
    scanf("%ld %ld",&a,&b);
    dis=h1;
    final1=h2;

    i=0;
    while(dis<=h2)
    {
        if(i==0)
        {
            dis=dis+8*a;
        }
        if(i>=1)
            dis=dis+(12*a);
        if(dis>=h2)
            break;
        dis=dis-(2*b);
        if(dis>=h2)
            break;
        i++;
        dis=dis-(10*b);
        if(dis>=h2)
            break;
        if(i>=100000)
        {
            printf("-1");
            return 0;
        }
    }
    printf("%ld",i);
    return 0;
}

#include<stdio.h>

int main()
{
    long long int i,h1,h2,a,b,dis,final1;
    scanf("%I64d %I64d",&h1,&h2);
    scanf("%I64d %I64d",&a,&b);
    dis=h1;
    final1=h2;
    if(a<b)
    {
        printf("-1");
        return 0;
    }
    for(i=0;;i++)
    {
        if(i==0)
        {
            dis+=8*a;
        }
        else
            dis+=12*a;
        if(dis>=final1)
            break;
        dis-=12*b;
    }
    printf("%I64d",i);
    return 0;
}

#include<stdio.h>

int main()
{
    long int i,h1,h2,a,b,dis,final1;
    scanf("%ld %ld",&h1,&h2);
    scanf("%ld %ld",&a,&b);
    dis=h1;
    final1=h2;

    i=0;
    while(dis<=h2)
    {
        if(i==0)
        {
            dis=dis+8*a;
        }
        if(i>=1)
            dis=dis+(12*a);
        if(dis>=h2)
            break;
        dis=dis-(2*b);
        if(dis>=h2)
            break;
        i++;
        dis=dis-(10*b);
        if(dis>=h2)
            break;
        if(i>=9999)
        {
            printf("-1");
            return 0;
        }
    }
    printf("%ld",i);
    return 0;
}

#include<stdio.h>

int main()
{
    long long int h1,h2,a,b,day;
    scanf("%I64d %I64d",&h1,&h2);
    scanf("%I64d %I64d",&a,&b);
    day=(a+b)/(h1+h2)+(a-b);
    printf("%I64d",day);
    return 0;
}

#include<stdio.h>

int main()
{
    int h1,h2,a,b,k,c=0;
    scanf("%d %d",&h1,&h2);
    scanf("%d %d",&a,&b);
    k=8*a;
    if(a-b>0){
            while(k<h2-h1){
                c++;
                k=k+12*(a-b);
            }

            printf("%d",c);

    }
    else if(a-b<0)printf("-1");
    else printf("0");

    return 0;
}

#include<stdio.h>

int main()
{
    int h1,h2,a,b;
    scanf("%d %d",&h1,&h2);
    scanf("%d %d",&a,&b);

    if(a-b>0)printf("1");
    else if(a-b<0)printf("-1");
    else printf("0");

    return 0;
}

#include <stdio.h>
#include <stdlib.h>
#include <math.h>
#include <string.h>

int main () {

	int a, b;
	int h1, h2;
	int i = 0;
	int j = 14;

	scanf("%d %d", &h1, &h2);
	scanf("%d %d", &a, &b);
// printf("%d %d\n", h1, h2);
// printf("%d %d\n", a, b);
	if (h1 + 8 * a >= h2) { //alcanca no 1 dia
		printf("0\n");
		return 0;
	}
	if (a < b) {
		printf("-1\n");
		return 0;
	}
// 	printf("#\n");
	while (1) {
// 		printf("%d %d\n", h1, h2);
		if (i == 5)
			break;
		if (10 <= j && j < 22) { //dia
			h1 += a * (22 - j);

			if (h1 >= h2) {
				printf("%d\n", i);
				break;
			}
			i++;
			j = 22;
		} else { //noite
			h1 -= b * (j - 10);
			j = 10;
		}
	}

	return 0;

}

#include <stdio.h>
#include <stdlib.h>
#include <math.h>
#include <string.h>

int main () {

	int a, b;
	int h1, h2;
	int i = 0;
	int j = 14;

	scanf("%d %d", &h1, &h2);
	scanf("%d %d", &a, &b);
// printf("%d %d\n", h1, h2);
// printf("%d %d\n", a, b);
	if (h1 + 8 * a >= h2) { //alcanca no 1 dia
		printf("0\n");
		return 0;
	}
	if (a < b) {
		printf("-1\n");
		return 0;
	}
// 	printf("#\n");
	while (1) {
// 		printf("%d %d\n", h1, h2);
		if (i == 5)
			break;
		if (10 <= j && j < 22) { //dia
			h1 += a * (22 - j);

			if (h1 >= h2) {
				if (h1 - 8 * a >= h2)
					i--;
				printf("%d\n", i);
				break;
			}
			i++;
			j = 22;
		} else { //noite
			h1 -= b * (j - 10);
			j = 10;
		}
	}

	return 0;

}

#include <stdio.h>
#include <stdlib.h>
#include <math.h>
#include <string.h>

int main () {

	long long a, b;
	long long h1, h2;
	long long res;

	scanf("%I64d %I64d", &h1, &h2);
	scanf("%I64d %I64d", &a, &b);
// printf("%d %d\n", h1, h2);
// printf("%d %d\n", a, b);
	if (h1 + 8 * a >= h2) { //alcanca no 1 dia
		printf("0\n");
		return 0;
	}
	if (a <= b) {
		printf("-1\n");
		return 0;
	}

	h1 += 8 * a;

	res = (h2 - h1) / ((a - b) * 12);

	h1 += res * (a - b) * 12;

	if (h1 >= h2) {
		if (h1 - 8 * a >= h2)
			res--;
		printf("%I64d\n", res);
	}
	h1 += (a - b) * 12;
	res++;
	if (h1 >= h2) {
		if (h1 - 8 * a >= h2)
			res--;
		printf("%I64d\n", res);
	}

	return 0;

}

#include <stdio.h>
#include <stdlib.h>
#include <math.h>
#include <string.h>

int main () {

	int a, b;
	int h1, h2;
	int i = 0;
	int j = 14;

	scanf("%d %d", &h1, &h2);
	scanf("%d %d", &a, &b);
// printf("%d %d\n", h1, h2);
// printf("%d %d\n", a, b);
	if (h1 + 8 * a >= h2) { //alcanca no 1 dia
		printf("0\n");
		return 0;
	}
	if (a <= b) {
		printf("-1\n");
		return 0;
	}
// 	printf("#\n");
	while (1) {
// 		printf("%d %d\n", h1, h2);

		if (10 <= j && j < 22) { //dia
			h1 += a * (22 - j);

			if (h1 >= h2) {
				if (h1 - 8 * a >= h2)
					i--;
				printf("%d\n", i);
				break;
			}
			i++;
			j = 22;
		} else { //noite
			h1 -= b * (j - 10);
			j = 10;
		}
	}

	return 0;

}

#include<stdio.h>
int main()
{
 int h1,h2;
 int a,b;
 scanf("%d %d",&h1,&h2);
 scanf("%d %d",&a,&b);

  if((h2-(h1+8*a))<1)
   printf("0\n");
   else if (a<=b)printf("-1\n");
   else {         int c=h2-h1-8*a;
	c/=12;
               printf("%d\n",c/(a-b)+1);
        }
  return 0;
}

#include<stdio.h>
#include<math.h>
#include<stdlib.h>
int main()
{
    int a,b,c,d,e,t,r=0,i;
    scanf("%d %d %d %d",&a,&b,&c,&d);

    i=8*c;
    e=b-a;
    t=12*(c-d);
    if(i>=e)
       r=0;
    else if(t<1)
        r=-1;
    else{
            r=(e/t);
        if((int)(e/t)==(e/t))
            r=r;
        else
            r++;
    }

    printf("%d",r);

return 0;
}

#include<stdio.h>
#define MOD 1000000007
typedef long long int llu;
llu mod(llu a) {
	return a>0?a:-1*a;
}
int main()
{
	llu h1,h2,a,b,i,ans=0;
	scanf("%I64d%I64d",&h1,&h2);
	scanf("%I64d%I64d",&a,&b);
	if(b>=a) {
		if( h2>8*a+h1 )
			ans = -1;
		else
			ans = 0;
	}
	else {
		if(h1+8*a>=h2) {
			ans = 0;
		}
		else {
			ans = (h2-(h1+8*a))/(12*(mod(b-a)));
			ans++;
		}
	}
	printf("%I64d",ans);
	return 0;
}

#include<stdio.h>
#define MOD 1000000007
typedef long long int llu;
int main()
{
	llu h1,h2,a,b,i,ans=0;
	scanf("%I64d%I64d",&h1,&h2);
	scanf("%I64d%I64d",&a,&b);
	if(b>=a) {
		if( h2>8*a+h1 )
			ans = -1;
		else
			ans = 0;
	}
	else {
		if(h1+8*a>=h2) {
			ans = 0;
		}
		else {
			ans = (h2-(h1+8*a))/(12*(b-a));
			ans++;
		}
	}
	printf("%I64d",ans);
	return 0;
}

#include<stdio.h>
int main(){
    int n,m,get,slip;
    while(scanf("%d%d%d%d",&n,&m,&get,&slip)!=EOF){
          if(n+8*get<m&&get<=slip)
            printf("-1\n");
            else{
                n=n+8*get;
                if(n>=m) {
                    printf("0\n");continue;
                }
                n=n-12*slip;
                if(n<0) n=0;
                for(int i=1;;i++){
                    n=n+get*12;
                    if(n>=m&&n-get*2>=m) {
                        printf("%d\n",i);
                       // printf("n=%d",n);
                        break;
                    }
                    n-=12*slip;
                    if(n<0) n=0;
                }
            }
          }
        return 0;
}

#include<stdio.h>
int main(){
    int n,m,get,slip;
    while(scanf("%d%d%d%d",&n,&m,&get,&slip)!=EOF){
          if(n+8*get>=m) {
            printf("0\n");continue;
          }
          else if(get<=slip){
            printf("-1\n");continue;
            }
          else printf("%d\n",(m-n-8*get+12*(get-slip)+1)/(12*(get-slip)));
          }
        return 0;
}

#include<stdio.h>
int main(){
    int n,m,get,slip;
    while(scanf("%d%d%d%d",&n,&m,&get,&slip)!=EOF){
          if(n+8*get<m&&get<=slip)
            printf("-1\n");
            else{
                n=n+8*get;
                if(n>=m) {
                    printf("0\n");continue;
                }
                n=n-12*slip;
                if(n<0) n=0;
                for(int i=1;;i++){
                    n=n+get*12;
                    if(n>=m&&n-get*2>=m) {
                        printf("%d\n",i);
                        printf("n=%d",n);
                        break;
                    }
                    n-=12*slip;
                    if(n<0) n=0;
                }
            }
          }
        return 0;
}

#include <stdio.h>
//#pragma warning (disable : 4996)
int main(int argc, char * argv[])
{
	long long int a, b; scanf("%lld %lld", &a, &b);
	long long int c, d; scanf("%lld %lld", &c, &d);

	a += c * 8;
	if (a >= b)
		printf("0\n");
	else if (c <= d)
		printf("-1\n");
	else
		printf("%lld\n", (b - a) / (c * 12 - d * 12) + 1);

	return 0;
}

#include <stdio.h>
//#pragma warning (disable : 4996)
int main(int argc, char * argv[])
{
	long long int a, b; scanf("%lld %lld", &a, &b);
	long long int c, d; scanf("%lld %lld", &c, &d);

	a += c * 8;
	if (a >= b)
		printf("0");
	else if (c <= d)
		printf("-1");
	else
		printf("%lld", (b - a) / ((c - d) * 12) + 1);

	return 0;
}

#include <stdio.h>
//#pragma warning (disable : 4996)
int main(int argc, char * argv[])
{
	long long int a, b; scanf("%lld %lld", &a, &b);
	long long int c, d; scanf("%lld %lld", &c, &d);

	a += c * 8;
	if (a >= b)
		printf("0");
	else if (c <= d)
		printf("-1");
	else
		printf("%lld", (((b - a) / ((c - d) * 12))) + 1);

	return 0;
}

#include <stdio.h>
//#pragma warning (disable : 4996)
int main(int argc, char * argv[])
{
	int a, b; scanf("%d %d", &a, &b);
	int c, d; scanf("%d %d", &c, &d);

	a += c * 8;
	if (a >= b)
		printf("0");
	else if (c <= d)
		printf("-1");
	else
		printf("%d", (((b - a) / ((c - d) * 12))) + 1);

	return 0;
}

#include <stdio.h>
//#pragma warning (disable : 4996)
int main(int argc, char * argv[])
{
	long long int a, b; scanf("%lld %lld", &a, &b);
	long long int c, d; scanf("%lld %lld", &c, &d);

	a += c * 8;
	if (a >= b)
		printf("0");
	else if (c <= d)
		printf("-1");
	else
		printf("%lld", ((b - a) / ((c - d) * 12)) + 1);

	return 0;
}

#include <stdio.h>
//#pragma warning (disable : 4996)
int main(int argc, char * argv[])
{
	int a, b; scanf("%d %d", &a, &b);
	int c, d; scanf("%d %d", &c, &d);
	int day = 0;
	a += 8 * c;
	while (1)
	{

		if (a >= b)
		{
			printf("%d", day);
			break;
		}
		if (b >= a)
		{
			printf("-1");
			break;
		}
		day++;
		a += 12 * c - 12 * d;

	}
	return 0;
}

# include <stdio.h>

int main ()
{
    int a,b,u,v;
    scanf("%d %d %d %d",&a,&b,&u,&v);
    int x=b-a;
    int z=12*v;
    int y=8*u;
    int w=12*u;
    if(u<v) {printf("-1"); return 0;}
    if(x<=(8*u)) {printf("0"); return 0;}
    else a=a+y-z;
    //if(a+y<0) printf("1") return 0;
    for(long int i=1;i<20000000000;i++){
        if(a<0 || a+w>=b)
            {printf("%ld",i);
                return 0;}
        else a=a+w-z;
    }
    printf("-1");
    return 0;
}

# include <stdio.h>

int main ()
{
    int a,b,u,v;
    scanf("%d %d %d %d",&a,&b,&u,&v);
    int x=b-a;
    int z=12*v;
    int y=8*u;
    int w=12*u;
    if(x<=(8*u)) {printf("0"); return 0;}
    if(u<v) {printf("-1"); return 0;}
    if(a+y-z < 0) {printf("1"); return 0;}
    else a=a+y-z;
    //if(a+y<0) printf("1") return 0;
    for(long int i=1;i<20000000000;i++){
        if(a<0 || a+w>=b)
            {printf("%ld",i);
                return 0;}
        else a=a+w-z;
    }
    printf("-1");
    return 0;
}

#include <stdio.h>

int main()
{
  int h1, h2, a, b, ans = 0;
  scanf("%d %d", &h1, &h2);
  scanf("%d %d", &a, &b);

  if (a <= b && h2 - h1 - a * 8 > 0) {
    printf("-1\n");
    return 0;
  }

  int dis = h2 - h1 - a * 8;
  if (dis <= 0) {
    printf("1\n");
    return 0;
  }
  ans += 1;

  while (dis > 0) {
    dis -= (a - b) * 12;
    if (dis <= 0) break;
    ans+= 1;
  }

  printf("%d\n", ans);
  return 0;
}

#include <stdio.h>

int main()
{
  int h1, h2, a, b, ans = 0;
  scanf("%d %d", &h1, &h2);
  scanf("%d %d", &a, &b);

  if (a <= b && h2 - h1 - a * 8 > 0) {
    printf("-1\n");
    return 0;
  }

  int dis = h2 - h1 - a * 8;
  if (dis <= 0) {
    printf("-1\n");
    return 0;
  }
  ans += 1;

  while (dis > 0) {
    dis -= (a - b) * 12;
    if (dis <= 0) break;
    ans+= 1;
  }

  printf("%d\n", ans);
  return 0;
}

#include<stdio.h>

int main()
{
	int a,b,h1,h2,i,j,k,count,sum;

	scanf("%d%d%d%d",&h1,&h2,&a,&b);

	h1=h2-h1;

	sum=a*(10-2);

	if(sum>=h1)
	{
		printf("0\n");
		return 0;
	}
	else
	{
		sum=sum-12*b;
		i=0;
		count=1;
		while(1)
		{
			sum=sum+4*a;

			if(sum<=h1&&sum+8*a>=h1)
			{
				printf("%d\n",count);
				break;
			}

			sum+=8*a;
			sum-=12*b;
			count++;
			if(count>=1000000)
			{
				printf("-1\n");
				break;
			}
		}
	}

	return 0;
}

#include<stdio.h>

int main()
{
	int a,b,h1,h2,i,j,k,count,sum;

	scanf("%d%d%d%d",&h1,&h2,&a,&b);

	h1=h2-h1;

	sum=a*(10-2);

	if(sum>=h1)
	{
		printf("0\n");
		return 0;
	}
	else
	{
		sum=sum-12*b;
		if(sum<=0)
			sum=0;

		i=0;
		count=1;
		while(1)
		{
			sum=sum+4*a;

			if(sum<=h1&&sum+8*a>=h1)
			{
				printf("%d\n",count);
				break;
			}

			sum+=8*a;
			sum-=12*b;
			if(sum<=0)
				sum=0;

			count++;
			if(count>=1000000)
			{
				printf("-1\n");
				break;
			}
		}
	}

	return 0;
}

#include<stdio.h>

int main()
{
	int a,b,h1,h2,i,j,k,count,sum;

	scanf("%d%d%d%d",&h1,&h2,&a,&b);

	h1=h2-h1;

	sum=a*(10-2);

	if(sum>=h1)
	{
		printf("0\n");
		return 0;
	}
	else if(a<=b)
	{
		printf("-1\n");
	}
	else
	{
		sum=sum-12*b;
		i=0;
		count=1;
		while(1)
		{
			sum=sum+4*a;

			if(sum<=h1&&sum+8*a>=h1)
			{
				printf("%d\n",count);
				break;
			}

			sum+=8*a;
			sum-=12*b;
			count++;
			if(count>=100000)
			{
				printf("-1\n");
				break;
			}
		}
	}

	return 0;
}

#include <stdio.h>

#define S_N 8
#define DN 12
#define D_S 4

int main() {

    int h1, h2;
    int a, b;

    scanf("%d%d", &h1, &h2);
    scanf("%d%d", &a, &b);

    h1 += S_N * a;
    if (h1 >= h2) {
        printf("0");
        return 0;
    }
    if (a <= b) {
        printf("-1");
        return 0;
    }
    printf("%d", (h2 - h1) / ((a - b) * DN) + 1);
    return 0;

}

#include<stdio.h>
int main()
{
    long long int x,y,a,b,i,l=0;
    scanf("%lld %lld",&x,&y);
    scanf("%lld %lld",&a,&b);
    if(8*a+x>=y)
    {printf("0");}
    else
    {if(b>=a)
     {printf("-1");}
     else
     {x=x+8*a-12*b;
      i=0;
      while(x<y)
      { i++;
        x=x+(12*a-12*b);
      }

      printf("%lld",i-1);
     }
    }
    return 0;
}

#include<stdio.h>
int main()
{
    long long int x,y,a,b,i,l=0;
    scanf("%lld %lld",&x,&y);
    scanf("%lld %lld",&a,&b);
    if(8*a+x>=y)
    {printf("0");}
    else
    {if(b>=a)
     {printf("-1");}
     else
     {x=x+8*a-12*b;
      i=0;
      while(x<y)
      { i++;
        x=x+(12*a);
        if(x>=y)
        {printf("%lld",i);}
        x=x-12*b;
      }
     }
    }
    return 0;
}

#include<stdio.h>
int main()
{
    long long int x,y,a,b,i,l=0;
    scanf("%lld %lld",&x,&y);
    scanf("%lld %lld",&a,&b);
    if(8*a+x>=y)
    {printf("0");}
    else
    {x=x+8*a-12*b;
     for(i=4;i<=12;i++)
     {if(x+i*a>=y)
      {l++;
       break;
      }
     }
     if(l==0)
     {printf("-1");}
     else
     {printf("1");}
    }
    return 0;
}

#include<stdio.h>
int main ()
{
	int h1,h2,a,b;
	scanf("%d %d",&h1,&h2);
	scanf("%d %d",&a,&b);
	if(a<b) printf("%d",-1);
	else if(h2-h1<8*a) printf("%d",0);
	else{
	h1=h1+a*8-b*12;
	int count=1;
	while(h1+12*a<h2){
		h1=a*12+h1-b*12;
		if(h1<0) break;
		count++;
	}
	printf("%d",count);}
	return 0;
}

#include<stdio.h>
int main ()
{
	int h1,h2,a,b;
	scanf("%d %d",&h1,&h2);
	scanf("%d %d",&a,&b);
	if(a<b) printf("%d",-1);
	else if(h2-h1<8*a) printf("%d",0);
	else{
	h1=h1+a*8-b*12;
	int count=1;
	while(h1+12*a<h2){
		h1=a*12+h1-b*12;
		count++;
	}
	printf("%d",count);}
	return 0;
}

#include<stdio.h>
int main ()
{
	int h1,h2,a,b;
	scanf("%d %d",&h1,&h2);
	scanf("%d %d",&a,&b);
	if(h2-h1<8*a) printf("%d",0);
	else if(a<b) printf("%d",-1);
	else{
	h1=h1+a*8-b*12;
	int count=1;
	while(h1+12*a<h2){
		h1=a*12+h1-b*12;
		if(h1<0) break;
		count++;
	}
	printf("%d",count);}
	return 0;
}

#include<stdio.h>
int main ()
{
	int h1,h2,a,b;
	scanf("%d %d",&h1,&h2);
	scanf("%d %d",&a,&b);
	if(h2-h1<8*a) printf("%d",0);
	else if(a<=b) printf("%d",-1);
	else{
	h1=h1+a*8-b*12;
	int count=1;
	while(h1+12*a<h2){
		h1=a*12+h1-b*12;
		count++;
	}
	printf("%d",count);}
	return 0;
}

# include <stdio.h>

int main ()
{
    int a,b,u,v;
    scanf("%d %d %d %d",&a,&b,&u,&v);
    int x=b-a;
    int z=12*v;
    int y=8*u;
    int w=12*u;
    if(u<v) {printf("-1"); return 0;}
    if(x<=(8*u)) {printf("0"); return 0;}
    else a=a+y-z;
    //if(a+y<0) printf("1") return 0;
    for(int i=1;i<1000;i++){
        if(a<0 || a+w>=b)
            {printf("%d",i);
                return 0;}
        else a=a+w-z;
    }
    printf("-1");
    return 0;
}

# include <stdio.h>

int main ()
{
    int a,b,u,v;
    scanf("%d %d %d %d",&a,&b,&u,&v);
    int x=b-a;
    int z=12*v;
    int y=8*u;
    int w=12*u;
    if(u<v) {printf("-1"); return 0;}
    if(x<=(8*u)) {printf("0"); return 0;}
    else a=a+y-z;
    //if(a+y<0) printf("1") return 0;
    for(int i=1;i<1000;i++){
        if(a<0 || a+w>=b)
            {printf("%d",i);
                return 0;}
        else a=a+w-z;
    }

    return 0;
}

# include <stdio.h>

int main ()
{
    int a,b,u,v;
    scanf("%d %d %d %d",&a,&b,&u,&v);
    int x=b-a;
    int z=12*v;
    int y=8*u;
    int w=12*u;
    if(x<=(8*u)) {printf("0"); return 0;}
    if(u<v) {printf("-1"); return 0;}

    else a=a+y-z;
    //if(a+y<0) printf("1") return 0;
    for(long int i=1;i<20000000000;i++){
        if(a<0 || a+w>=b)
            {printf("%ld",i);
                return 0;}
        else a=a+w-z;
    }
    printf("-1");
    return 0;
}

#include <stdio.h>
#include <string.h>
#include <stdbool.h>

#define clr(ar) memset(ar, 0, sizeof(ar))
#define read() freopen("lol.txt", "r", stdin)

int main(){
    int i, j, k, l, x, h1, h2, a, b;

    while (scanf("%d %d %d %d", &h1, &h2, &a, &b) != EOF){
        int hour = 14, days = 0, lim = 1e8;

        while (h1 < h2 && lim--){
            if (hour >= 10 && hour < 22) h1 += a;
            else h1 -= b;
            hour++;
            if (hour == 24) hour = 0;
            if (hour == 10) days++;
        }

        if (lim <= 0) days = -1;
        printf("%d\n", days);
    }
    return 0;
}

#include<stdio.h>
#include<string.h>
int main()
{
	int s,e;
	int u,d;
	int len;
	int day=0,flag=1;
	scanf("%d %d",&s,&e);
	scanf("%d %d",&u,&d);
	len=e-s;
	if(u*6>=len) printf("0\n");
	else if(u<=d) printf("-1\n");
	else
	{
		day=0;flag=1;
		len=len-u*6;
		while(flag==1)
		{
			len-=12*u;
			day++;
			if(len<=0) flag=0;
			len+=12*d;
		}
		printf("%d\n",day);
	}
}

#include <stdio.h>

/*
 * http://codeforces.com/problemset/problem/652/A
 */
int main()
{
    int hc = 0, ha = 0;
    scanf("%d %d", &hc, &ha);

    int a = 0, b = 0, d = 0;
    scanf("%d %d", &a, &b);

    hc += 8 * a;

    if (hc < ha && a <= b) {
        printf("-1\n");

        return 0;
    }

    while (hc <= ha) {
        hc += a * 12 - b * 12;
        d += 1;
    }

    printf("%d\n", d);

    return 0;
}

#include<stdio.h>
#include<stdbool.h>

int main(){
    long long int h1,h2,a,b;
     scanf("%lld %lld",&h1,&h2);
     scanf("%lld %lld",&a,&b);
     int i;
     long long int dist=h1;
     bool day=1,first=1,sec=1;
     int count=0;
      while(1){
           if(dist>=h2||(!sec&&dist<0))
            break;
           if(day&&first){
            dist+=(a*8);
            day=0;
            first=0;
           }
           else if(!day){
            dist-=(b*12);
            count++;
            day=1;
           }
           else if(!first){
               dist+=(a*12);
               day=0;
               sec=0;
           }

      }
      if(dist>=h2)
      printf("%d",count);
      else
      printf("-1");
}

#include <stdio.h>
#include <stdlib.h>
#include <math.h>

int main()
{
    long long h1,h2,a,b,h,step,days;

    scanf("%lld %lld",&h1,&h2);
    scanf("%lld %lld",&a,&b);

    if(b>a && (8*a)<(h2-h1))
        printf("-1");

    else if(8*a >= h2-h1)
        printf("0");

    else
    {
        h = h2 - (h1 + 8*a);
        step = 12*(a-b);
        days = ceil((double)h/step);
        printf("%lld",days);
    }

    return 0;
}

#include<stdio.h>
int main(){
    int a,b,c,d,e,f,g;
    int first,second;
    int up,down;
    scanf("%d%d",&first,&second);
    scanf("%d%d",&up,&down);
    if(((first + 8*up) - (12 * down) + 4*up) <= first && (((8*up)+first) <= second)){
    printf("-1");
    return 0;}
    if(up == down && (((8*up)+first) <= second)){
    printf("-1");
    return 0;
    }
    int cnt=0,i;
    if(first>=second){
    printf("0");
    return 0;}
    while(1){
    for(i=0;i<8;i++){
    first+=up;
    if(first>=second){
    printf("%d",cnt);
    return 0;
    }}
    for(i=0;i<12;i++){
    first-=down;
    if(first>=second){
    printf("%d",cnt);
    return 0;
    }}
    cnt++;
    for(i=0;i<4;i++){
    first+=up;
    if(first>=second){
    printf("%d",cnt);
    return 0;
    }}
    }
}

#include <stdio.h>
#include <stdlib.h>

int main()
{
    int h,h1,h2,a,b,up,down,reach,des;
    int k=-1;
    scanf("%d%d",&h1,&h2);
    scanf("%d%d",&a,&b);
   h=h2-h1;
      up=12*a;
   down = 12*b;
   if(a==b)
   {    k=0;
       printf("%d",k);
       return 0;
   }

    reach=up-down;
     k=h/reach;

    if(b>a)
    {   k=-1;
        printf("%d",k);
        return 0;
    }

    else if((reach>h) ||  (des<0))
    {   k=0;
        printf("%d",k);
         return 0;
    }

    if(k>1)
        k=1;
      printf("%d",k);

    return 0;
}

#include<stdio.h>

int cat(int a,int b,int h1, int h2,int d)
{   int pos=0,k=0;
       pos=(a*8)+h1;
    if(pos>=h2)
    {
        k=d;
        printf("%d",k);
        return 0;
    }
    d++;
    pos-=(b*12);
    pos=pos+a*4;
     if(pos>=h2)
    {
        k=d;
        printf("%d",k);
        return 0;
    }
    cat(a,b,pos,h2,d);
}

int main()
{
    int a,b,h1,h2,d=0;
    scanf("%d%d",&h1,&h2);
    scanf("%d%d",&a,&b);
	if(a==b)
	{
	printf("%d",d);
	return 0;
	}
	if(a<b)
	{
	d=-1;
	printf("%d",d);
	return 0;

	}

cat(a,b,h1,h2,d);
return 0;
}

#include<stdio.h>
int main()
{
	int e;
	float a,g,b,c,d;
	scanf("%f%f%f%f",&a,&b,&c,&d);
	if(a+8*c>=b || a==b)
	{
		printf("0\n");
		goto jump;
	}
	else if(c<d || (c==d && a!=b))
	{
		printf("-1\n");
		goto jump;
	}
	else
	{
		e=2*(b-a-8*c)/(c-d);
		g=2*(b-a-8*c)/(c-d);
	}
	int f=e%24;
	if(f<=2 && g<=2)
	{
		printf("%d\n",e/24);
	}
	else
		printf("%d\n",e/24+1);
	jump:
	return 0;
}

#include<stdio.h>
int main()
{
	int e;
	float a,g,b,c,d;
	scanf("%f%f%f%f",&a,&b,&c,&d);
	if(a+8*c>=b || a==b)
	{
		printf("0\n");
		goto jump;
	}
	else if(c<d || (c==d && a!=b))
	{
		printf("-1\n");
		goto jump;
	}
	else
	{
		e=2*(b-a-8*c)/(c-d);
		g=2*(b-a-8*c)/(c-d);
	}
	int f=e%24;
	if(f!=0)
	printf("%d\n",e/24+1);
else printf("%d\n",e/24);
	jump:
	return 0;
}

#include<stdio.h>
int main()
{
	int a,b,c,d,e;
	scanf("%d%d%d%d",&a,&b,&c,&d);
	if(a+8*c>=b || a==b)
	{
		printf("0\n");
		goto jump;
	}
	else if(c<d || (c==d && a!=b))
	{
		printf("-1\n");
		goto jump;
	}
	else
	{
		e=2*(b-a-8*c)/(c-d);
	}
	int f=e%24;
	if(f<=2)
	{
		printf("%d\n",e/24);
	}
	else
		printf("%d\n",e/24+1);
	jump:
	return 0;
}

#include<stdio.h>
int main()
{
	int e;
	float a,g,b,c,d;
	scanf("%f%f%f%f",&a,&b,&c,&d);
	if(a+8*c>=b || a==b)
	{
		printf("0\n");
		goto jump;
	}
	else if(c<d || (c==d && a!=b))
	{
		printf("-1\n");
		goto jump;
	}
	else
	{
		e=2*(b-a-8*c)/(c-d);
		g=2*(b-a-8*c)/(c-d);
	}
	int f=e%24;
	if(f==0 || g<=2)
	printf("%d\n",e/24);
else if(f!=0)
	printf("%d\n",e/24+1);
	jump:
	return 0;
}