杭电oj 1001

#include<iostream>
using namespace std;
int main()
{
    int n = , sum;
    while (cin>>n)
    {
        sum = ; // 这里要清零
        for (int i =; i <= n; i++)
        {
            sum += i;
        }
        cout << sum <<endl <<endl;
    }
    return ;
}