#include <stdio.h>
#include <string.h>
#include <stdlib.h>

using namespace std;

//遅刻　namaega184

int main(){
	
	double pi=3.14159265;
	double n,a,b;scanf("%lf%lf%lf",&n,&a,&b);
	double c=(b+a)*0.5,d=(b-a)*0.5;
	printf("%.5f",n*c*d*d*pi*pi*2); 
	
	return 0;
}