title: Store/output a number bigger than unsigned long long can store
body: <p>With user given number (n) for example n=5, I calculate the sum of 10000,10001,10002....99999.
  Works up until n=17, then I get a negative number or eventually a zero.</p>
  <p>So my question is how do I store a number bigger than unsigned long long lets me</p>
  <pre><code>#include &lt;iostream&gt;
  #include &lt;iomanip&gt;
  #include &lt;cmath&gt;
  
  using namespace std;
  int main() 
  {
    unsigned long long n, sum;
    cin&gt;&gt;n;
    unsigned long long start=pow(10, n-1);
    unsigned long long finish=pow(10, n)-1;
    sum=((finish-start+1)*(start+finish))/2;
    cout&lt;&lt;sum&lt;&lt;endl;
    return 0;
  }
  </code></pre>