#include <iostream>
#include <stdio.h>
using namespace std;
double PI=3.1415926;
int main(int argc, char* argv[])
{
	int C;
	int Rin,Rout;
	cin>>C;
	cin>>Rin>>Rout;
	double H=(Rin+Rout)*PI;
	
	double A=(Rout-Rin)*(Rout-Rin)*PI;

	double V=A*H/4;
	printf("%.10lf",C*V);
	return 0;
}