합

#include <iostream>
using namespace std;

int main(void)
{
   int num = 0, sum = 0;

   cin >> num;
   if (num < 1 || 10000 < num)
      return 0;

   for (int i = 0; i <= num; i++)
   {
      sum += i;
   }

   cout << sum << '\n';
   return 0;
}