#include<iostream>
#include<iomanip>

static const double PI = 3.1415926535897;

int main() {
	double kcal, inside_radius, outside_radius;

	std::cin >> kcal >> inside_radius >> outside_radius;

	double radius = (outside_radius - inside_radius) / 2;
	double circle_area = radius * radius * PI;
	double torus = 2 * PI * (radius + inside_radius) * circle_area;

	std::cout << std::fixed << std::setprecision(7) << kcal * torus  << std::endl;
	return 0;
}