文件目录

#include <iostream>
using namespace std;
int main()
{
    int n;
    cin >> n;
    cout << (1 + n) * n / 2;
    return 0;
}
int ans1()
{
    int n, s = 0;
    cin >> n;
    for (int i = 1; i <= n; i++)
        s += i;
    cout << s;
    return 0;
}