#include <stdio.h>
#include <math.h>

int main() {
	int c, in, out;
	double r, v;
	const double pi = 3.14159265358979;

	scanf("%d %d %d", &c, &in, &out);

	r = (out - in) / 2.0;
	v = pow(r, 2.0) * pi * (in + r) * 2 * pi;
	
	printf("%lf", c * v);

	return 0;
}