#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;
#ifdef M_PI
	largeR = (rin + smallR) * 2.0 * M_PI;
	cal = smallR * smallR * M_PI * largeR * c;
#else
	largeR = (rin + smallR) * 2.0 * 3.141592;
	cal = smallR * smallR * 3.141592 * largeR * c;
#endif

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