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

void fast_io() {
	ios_base::sync_with_stdio(false);
	cin.tie(nullptr);
}

int main() {
	fast_io();
	unsigned long long n;
	cin >> n;
	if (n % 2 == 0) {
		cout << n / 2 * (n + 1) << endl;
	} else {
		cout << (n + 1) / 2 * n << endl;
	}
}