#include<bits/stdc++.h>
using namespace std;
int main() {
	using ull = unsigned long long;
	ull ans = 0, n = 0;
	cin >> n;
	if (n % 2LL == 0) ans = (n / 2LL) * (n + 1LL);
	else ans = n * ((n + 1) / 2);
	cout << ans << endl;
}