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

int main(void)
{
	char c,rin,rout;
	double smallR,largeR,cal;
	scanf("%hhd",&c);
	scanf("%hhd %hhd",&rin,&rout);

	smallR = (rout - rin) / 2.0;
	largeR = (rin + smallR) * 2.0 * M_PI;

	cal = smallR * smallR * M_PI * largeR * c;

	printf("%f\n",cal);
	
	return 0;
}