#include <iostream>
#include <iomanip>

using namespace std;

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

	double R, r, two, doubleC;
	two = 2.000000000000;
	doubleC = C;
	double P = 3.14159265358979;
	R = (double)( Ri + Ro ) / 2;
	r = R - (double)Ri;

	cout << setprecision(20) << (P*P*r*r*R)*two*doubleC << endl;

	return 0;
}