#include <bits/stdc++.h>
using namespace std;

int main()
{
double C;
double Rin;
double Rout;
double R;

	cin >> C;
	cin >> Rin;
	cin >> Rout;

	R = ( Rout - Rin ) / 2;

	cout << R * R * ( Rout + Rin ) *
		3.1415926535 * 3.1415926535 * C << endl;

	return 0;
}