package net.ipipip0129.yukicoder.no89;

import java.util.Scanner;

public class Main {
    public static void main(String[] args) {
        Scanner scan = new Scanner(System.in);

        int cal = Integer.parseInt(scan.nextLine());

        String[] data = scan.nextLine().split(" ");

        int rin = Integer.parseInt(data[0]);
        int rout = Integer.parseInt(data[1]);

        double doughnut = 0.25 * Math.pow(Math.PI, 2) * (rin + rout) * Math.pow((rout - rin), 2);

        System.out.println(doughnut * cal);
    }
}