#include <iostream>
#include <algorithm>
using namespace std;
int main() {
	cin.tie(0); ios::sync_with_stdio(false);
	long long N, ans = 0; cin >> N;
	for (long long n = 1; n <= N / 2;n++) {
		//ans = max(ans, n*(N - n) + n + (N - n));
		ans = max(ans, N*n + N - n*n);
	}
	cout << ans << endl;
	return 0;
}