#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, dist, len, sum, vol;
	scanf("%lf %lf %lf", &C, &Rin, &Rout);
	//cin >> C >> Rin >> Rout;
	rad = (Rout - Rin) / 2;
	sum = pow(rad, 2) * M_PI;
	dist = rad + Rin;
	len = dist * 2 * M_PI;
	vol = len * sum;
	printf("%f\n", vol * C);
	return 0;
}