#include<iostream>
#include<iomanip>
#include<cmath>

const double pi = acos(-1);

int main()
{
	double C, Ri, Ro;
	std::cin >> C >> Ri >> Ro;

	std::cout << std::fixed << std::setprecision(10) << pi*(Ri+Ro)*pi*(Ro-Ri)*(Ro-Ri)/4*C << std::endl;

	return 0;
}