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

int main(){
	double C,R_in,R_out;
	cin >> C >> R_in >> R_out;
	double x = (R_out - R_in) / 2.0; 
	double x_menseki = x * x * M_PI;
	double y_menseki = (R_in + x) * 2.0 * M_PI;
	double torus = x_menseki * y_menseki;
	double total = torus * C;
	printf("%.10lf\n",total);
	return 0;
}