#include <iostream>
using namespace std;
int main() {
	long L;
	long long ans = 0;
	cin >> L;
	/*
	for (int i = 1;i <= L / 2;i++) {
		ans += (2 * i -1);
	}

	n: 1 ～ k    ans = Σ(2k - 1)
	   a(n) = a(0) + (n - 1)*d
	   a(0) = 1 / d = 2 / n = L/2
	   S(n) = ans = 1/2 * n * (a(0) + a(n)) = 1/2 * n * {2a(0) + (n - 1)d}
	*/
	ans = (L / 2 * (2 + (L / 2 - 1) * 2)) / 2;
	cout << ans << endl;
	return 0;
}