杭电ACM1001

杭电ACM1001

#include <iostream>
int main()
{
 using namespace std;
 long int n,m;
 long int s;
 while (cin >> n)
 {
  if (n%2 == 0)
  {
   s = n/2*(n+1);
  }
  else
  {
   s = (n+1)/2*n;
  }
  cout  << s << endl << endl;
 }
 return 0;
}