using System;

public class Program

{

    public interface IThing

    {

        string Thingy();

    }

    public class MyBase : IThing

    {

        public virtual string Thingy()

        {

            return "base";

        }

    }

    public class DerivedOne : MyBase

    {

        public new string Thingy()

        {

            return "DerivedOne";

        }

    }

    public class DerivedTwo : MyBase

    {

        public override string Thingy()

        {

            return "DerivedTwo";

        }

    }

    public class DerivedThree : MyBase, IThing

    {

        public new string Thingy()

        {

            return "DerivedThree";

        }

    }

    public static void Main()

    {

        IThing b = new MyBase();

        IThing d1 = new DerivedOne();

        IThing d2 = new DerivedTwo();

        IThing d3 = new DerivedThree();

        Console.WriteLine(b.Thingy());

        Console.WriteLine(d1.Thingy());

        Console.WriteLine(d2.Thingy());

        Console.WriteLine(d3.Thingy());

    }

}