using System;

public class Program

{

    public class DrawingBase

    {

        // In base class if we declare methods with virtual keyword then only we can override 

        // those methods in derived class using override keyword

        public virtual void Draw()

        {

            Console.WriteLine("I'm just a generic drawing object.");

        }

    }

    // Derived Class

    public class Line : DrawingBase

    {

        public override void Draw()

        {

            Console.WriteLine("I'm a Line.");

        }

    }

     // Derived Class

    public class Circle : DrawingBase

    {

        public override void Draw()

        {

            Console.WriteLine("I'm a Circle.");

        }

    }

     // Derived Class

    public class Square : DrawingBase

    {

        public override void Draw()

        {

            Console.WriteLine("I'm a Square.");

        }

    }

    public static void Main()

    {

        // Parent class

        DrawingBase drawing = new DrawingBase();

        drawing.Draw();

        // Derived Class

        drawing = new Line();

        drawing.Draw();

        drawing = new Square();

        drawing.Draw();

        drawing = new Circle();

        drawing.Draw();

    }

}