import java.util.Scanner;

public class pre {
    public static void main(String[] args) {

        Scanner s = new Scanner(System.in);
		double c = s.nextDouble(),r = s.nextDouble(),R = s.nextDouble();
		double V = 2 * Math.pow(Math.PI,2) * Math.pow((R-r)/2,2) * (R-((R-r)/2));
		System.out.println(c * V);
    }
}