#include <iostream>
#include <iomanip>

int main() {
    int n;
    std::cin >> n;
    double side_length = static_cast<double>(n) / 4;
    double area = side_length * side_length;
    std::cout << std::fixed << std::setprecision(2) << area << std::endl;
    return 0;
}    
/**************************************************************
	Problem: 1420
	User: linmiaoling
	Language: C++
	Result: Accepted
	Time:6 ms
	Memory:2072 kb
****************************************************************/