#include <bits/stdc++.h>
#define PI 3.14159265359
using namespace std;
const int64_t MOD = 1e9 + 7;

int main() {
	int64_t L;
	cin >> L;

	int64_t a, b;
	a = 0;
	b = 0;

	for (int i = L / 2; i > 0; i--) {
		a += i;
	}

	for (int i = L / 2 - 1; i > 0; i--) {
		b += i;
	}

	cout << a + b << endl;
}