#include <iostream>
#include <vector>
#include <cmath>
#include <cstdlib>
#include <algorithm>
#include <string>
#include <queue>
#include <numeric>
#include "bits/stdc++.h"
using namespace std;

#define INF 100000000

int main() {
    int N;
    cin >> N;
    int sum = 0;
    for (int i = 1; i <= N; i++) {
        sum += i;
    }
    cout << sum << endl;
}