#include <bits/stdc++.h>
#include <atcoder/all>
using namespace std;
using ll = long long;
using ull = unsigned long long;
using mint = atcoder::modint998244353;
using maxt = atcoder::modint1000000007;

int main() {
	ull N;
	cin >> N;
	if(N % 2 == 0) {
		cout << N / 2 * (N + 1) << endl;
	}
	else {
		cout << (N + 1) / 2 * N << endl;
	}
}