#include <iostream>
using namespace::std;

int main() {
    int x = 0;
    int n;
    cin >> n;
    int m = 0;
    if (m<n && n<=100 && n>=1) {
        for(m==1; m<=n; ++m) {
            x += m;
        }
    cout << x << endl;
    }
}