#include <bits/stdc++.h>
using namespace std;
using ll = long long;
#define rep(i, s, e) for (int i = (int)s; i < (int)e; ++i)
#define all(a) (a).begin(), (a).end()

int main() {
    cin.tie(nullptr);
    
    unsigned long long N;
    cin >> N;
    
    if (N % 2 == 0) cout << N / 2 * (N + 1) << '\n';
    else cout << (N + 1) / 2 * N << '\n';
}