import java.util.Scanner;

public class No89 {
	public static void main(String[] args) {
		Scanner sc = new Scanner(System.in);
		int C = sc.nextInt();
		double r1 = sc.nextDouble();
		double r2 = sc.nextDouble();
		double V = Math.pow(Math.PI,2) * Math.pow((r2 - r1), 2) * (r1+r2) /4;
		
		System.out.println(C * V);
	}
}