#include <bits/stdc++.h>
#pragma GCC target("avx2")
#pragma GCC optimize("O3")
#pragma GCC optimize("unroll-loops")
#pragma GCC target("sse,sse2,sse3,ssse3,sse4,popcnt,abm,mmx,avx,tune=native")
using namespace std;
int main() {
    unsigned long long N;
    cin >> N;
    unsigned long long ans = 0;
    for (unsigned long long i = 1; i <= N; i++) {
        ans += i;
    }
    cout << ans << '\n';
}