#include <bits/stdc++.h>
#pragma GCC target("avx2")
#pragma GCC optimize("O3")
#pragma GCC optimize("unroll-loops")
using namespace std;

int main() {

	int n;
	cin >> n;
	
	unsigned long long ans = 0;
	for(int i=0;i<=n;++i) ans += i;
	cout << ans << endl;
}