#include<iostream>
#include<cstdio>
#include<cmath>

using namespace std;

#define NMAX 1000000

int main(){

	double C,Rin,Rout;
	double PI=acos(-1.0);

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

	double A=(Rout-Rin)/2;
	double B=Rout-A;

	printf("%.10f\n",C*2*A*A*B*PI*PI);
}