/**
*    author:  boutarou
*    created: 02.08.2020 10:52:54
**/

#include <bits/stdc++.h>
using namespace std;
#define rep(i,n) for(int i = 0; i < int(n); i++)
using ll = long long;
using P = pair<int, int>;

int main() {
    int n;
    cin >> n;
    cout << n * (n + 1) / 2 << endl;
    return 0;
}