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

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

	int max = 0;
	for (int x = 0;x <= d / 2;x++) {
		for (int y = 0;y <= d / 2;y++) {
			if (max < x*y && 2 * x + 2 * y <= d) {
				max = x * y;
			}
		}
	}
	cout << max << endl;

	return 0;
}