#include <stdio.h>
#define PI	(3.141592653589793)

int main(void){
	int a,b,c;
	double volume = 0.0;
	scanf("%d", &c);
	scanf("%d %d", &a, &b);
	
	volume = (1.0*(a+b)*(b-a)*(b-a)*PI*PI)/4.0;
	
	printf("%f\n", volume*(1.0*c));
	return 0;
}