#include<iostream>

using namespace std;

int main()
{
	int C, Rin, Rout;
	const double PI = 3.1415926535;
	double donutin, donutout, cal, d1;

	cin >> C >> Rin >> Rout;

	d1 = (double)((Rout - Rin) / 2.0);
	cal = (d1*d1*PI) *
			((d1 + (double)Rin) * 2.0 * PI) *
			  (double)C;

	cout << cal << endl;
}