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

using namespace std;

int main(int argc, const char* argv[])
{
	double C, Rin, Rout;
	cin >> C >> Rin >> Rout;
	cout << fixed << setprecision(5) << C * (Rout + Rin) * (Rout - Rin) * (Rout - Rin) * M_PI * M_PI / 4 << endl;
	return 0;
}