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

#define READ_BUFSIZE ( 1024 )
#define READ_DELIMITER ( " " )


int main(int argc, char *argv[]) 
{
	int C = 0;
	scanf("%d", &C);

	int Rin = 0;
	int Rout = 0;
	scanf("%d %d", &Rin, &Rout);

	double pi = acos(0) * 2;

	double V = pi * pi * (Rin + Rout)* ((Rout - Rin)*(Rout - Rin)) / 4 * C;

	printf("%lf\n", V);


	return 0;

}