using System;

public class Program

{

    public static void Main()

    {

        double r;

        const double Pi = 3.141592653589793238462;

        char opt;

        start:

        Console.Clear();

        Console.WriteLine(" Enter the value of Radius: ");

        r = Convert.ToDouble(Console.ReadLine());

        r=r*r;

        Console.WriteLine(4 * Pi * r);

        Console.WriteLine(4 * Pi * r);

        Console.WriteLine(" Do you want to try again [Y/N] ");

        opt = Convert.ToChar(Console.ReadLine());

        if (opt =='Y' || opt == 'y')

        goto start;

        else

        {

        Environment.Exit(0);

        }

    }

}