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

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

int main() {
	ll N;
	cin >> N;
	ll ans = 0;
	for(int i = 1; i < N; i++) {
		ans = max(ans, i + (N - i) * (i + 1));
	}
	cout << ans << endl;
}