#include <bits/stdc++.h>
using namespace std;

#define rep(i, n) for( ll i = 0; i < n; i++ )
using ll = unsigned long long;

int main() {
	ll N;
	cin >> N;
	__int128 n = N;
	ll ans = n * (n + 1) / 2;
	cout << ans << endl;
}