using System;

public class Program

{

    public static void Main()

    {

        Console.WriteLine("Hello World");

        var sq = new Square(12);        

        Console.WriteLine($"Area of the square = {sq.GetArea()}");

        Console.WriteLine($"Area of the square = {sq.GetVolume()}");

    }

    abstract class Shape

{

    public abstract int GetArea();

}

abstract class ShapeE : Shape

{   

    public abstract int GetVolume();

}

class Square : ShapeE

{

    private int _side;

​

    public Square(int n) => _side = n;

​

    // GetArea method is required to avoid a compile-time error.

    public override int GetArea() => _side * _side;

    public override int GetVolume() => _side * _side * _side;

}

}