#include <iostream>
#include <stdio.h>
#include <cmath>

#define FOR(i, a, b) for (int i = a; i < b; i++)
#define FORN(i, a, b) for (int i = a; i <= b; i++)
#define P(s) cout << s << endl
#define PC(condition, _true, _false) if (condition) _true; else _false;

using namespace std;
//
// Created by karayuu on 2019-02-16.
//

int main() {
    int n;
    cin >> n;
    
    P((1 + n) * n / 2);
}