#define _USE_MATH_DEFINES
#include <stdio.h>
#include <math.h>
int main(void){
	int C;
	int Rin;
	int Rout;
	double V;
	double r;
	double R;
	
	scanf("%d %d %d",&C,&Rin,&Rout);
	
	r = (double)(Rout - Rin) / 2;
	R = (double)(Rout - r);
	
	V = (double)2 * pow(M_PI * r,2) * R;
	
	printf("%lf\n",(double)V*C);
	return 0;
}