#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;

	std::cout << std::fixed << std::setprecision(7) << kcal * PI * PI / 4 * (inside_radius + outside_radius) *
		(outside_radius - inside_radius) * ((outside_radius - inside_radius)) << std::endl;
	return 0;
}