杭电oj 1001

#include<iostream>

using namespace std;

int main()

{

    int n = 0, sum;

    while (cin>>n)

    {

        sum = 0; // 这里要清零

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

        {

            sum += i;

        }

        cout << sum <<endl <<endl;

    }

    return 0;

}