#include <bits/stdc++.h>

using namespace std;

#ifdef LOCAL
#include "algo/debug.h"
#else
#define debug(...) (void(0))
#endif

void solve() {
    unsigned long long N; cin >> N;
    cout << N * (N + 1) / 2 << endl;
}

int main() {
    std::ios::sync_with_stdio(false);
    std::cin.tie(nullptr);
    int tt = 1;
    // std::cin >> tt;
    while(tt--) {
        solve();
    }
}