#include <iostream>
#include <cstdio>
#include <vector>
#include <algorithm>
#include <utility>

using namespace std;

int main() {
	int n;
	cin >> n;

	long long ans = 0;
	long long val;
	for (int i = 1; i < n; i++) {
		val = (1LL + i) * (n - i) + i;
		ans = max(ans, val);
	}

	cout << ans << endl;
	return 0;
}