#include <stdio.h>
#include <math.h>
int main(void){
	int C;
	int Rin;
	int Rout;
	double V;
	int pi = 3.141593;
	
	scanf("%d %d %d",&C,&Rin,&Rout);
	
	V = (double)0.5 * pi * pi * (Rout - Rin) * (Rout - Rin) * Rout;
	
	printf("%lf\n",V*C);
	return 0;
}