using System;

public class Program

{

    public class ReadOnlyModel

    {

    }

    public class Model : ReadOnlyModel

    {

        public void Write()

        {

            Console.WriteLine("Write operation performed!");

        }

    }

    public static void Main()

    {

        var readOnlyModel = new ReadOnlyModel();

        ((Model)readOnlyModel).Write(); // Run-time exception: Unable to cast object of type 'ReadOnlyModel' to type 'Model'.

        //Model model = readOnlyModel; // Compilation error: Cannot implicitly convert type 'Program.ReadOnlyModel' to 'Program.Model'.

        //model.Write();

        //readOnlyModel.Write(); // Compilation error: 'Program.ReadOnlyModel' does not contain a definition for 'Write'

    }

}