#include <iostream>
#include <iomanip>

const double PI = 3.14;

int main() {
    double x;
    std::cin >> x;

    double radius = x / (2 * PI);
    double area = PI * radius * radius;

    std::cout << std::fixed << std::setprecision(2) << area << std::endl;
    return 0;
}    
/**************************************************************
	Problem: 1337
	User: linmiaoling
	Language: C++
	Result: Accepted
	Time:8 ms
	Memory:2072 kb
****************************************************************/