#include<iostream>

using namespace std;

int main()
{
	int C, Rin, Rout;
	const double PI = 3.1415;
	double donutin, donutout, cal;

	cin >> C >> Rin >> Rout;

	cal = (double)((double)((Rout - Rin) / 2)*(double)((Rout - Rin) / 2)*PI) *
			(double)((double)((Rout - Rin) / 2 + Rin) * 2 * PI) *
			  (double)C;

	cout << cal << endl;
}