import java.util.Scanner;

public class No89 {

    public static void main(String[] args) {
        Scanner sc = new Scanner(System.in);
        double c = sc.nextDouble();
        double rIn = sc.nextDouble();
        double rOut = sc.nextDouble();

        double volume = (1d / 4d) * Math.pow(Math.PI, 2) * (rIn + rOut) * Math.pow((rOut - rIn), 2);
        double cal = c * volume;

        System.out.println(cal);

        sc.close();
    }

}