#include <cstdio>
#include <cstdlib>
#include <cstddef>
#include <vector>
#include <algorithm>
#include <cmath>
#include <string>
#include <iostream>
#include <iomanip>

int main(void)
{
	long a;
    std::cin >> a;
    a = (a - 1) / 2;
    std::cout << a * a << std::endl;
	return 0;
}