#define _USE_MATH_DEFINES
#include <stdio.h>
#include <iostream>
#include <math.h>
using namespace std;

int main(int argc, char *argv[]) {
	double C, Rin, Rout, rad;
	scanf("%lf %lf %lf", &C, &Rin, &Rout);
	rad = (Rout - Rin) / 2;
	printf("%f\n", (rad + Rin) * 2 * (rad * rad) * (M_PI * M_PI) * C);
	return 0;
}