#include <iostream>
#include <iomanip>

int main() {
    double x;
    std::cin >> x;
    double radius = x / (2 * 3.14);
    double area = 3.14 * radius * radius;
    std::cout << std::fixed << std::setprecision(2) << area;
    return 0;
}    
/**************************************************************
	Problem: 1337
	User: fuyijun
	Language: C++
	Result: Accepted
	Time:8 ms
	Memory:2072 kb
****************************************************************/