#include <iostream>
#include <cmath>
#include <iomanip>
int main() {
	double outer_r, inner_r, c;
	std::cin >> c >> outer_r >> inner_r;
	double R{ (outer_r + inner_r) / 2 }, r{ (outer_r - inner_r) / 2 };
	std::cout << std::setprecision(15) << c * r * r * R * std::acos(-1) * std::acos(-1) * 2 << std::endl;
	return 0;
}