#include<stdio.h>
#define PI 3.1415926535897932384626433832

int main(void){
	double c,ri,ro,d;
	scanf("%lf%lf%lf",&c,&ri,&ro);
	d = ((ro-ri)/2)*((ro-ri)/2)*PI;
	printf("%lf\n",2*PI*(ri+((ro-ri)/2))*d*c);
	return 0;
}