using System;

​

interface IPen

{

    string Color { get; set; }

    bool Open();

    bool Close();

    void Write(string text);

}

​

class Cello : IPen

{

    public string Color { get; set; }

    private bool isOpen = false;

    public bool Close()

    {

        isOpen = false;

        Console.WriteLine("Cello closed for writing!");

​

        return isOpen;

    }

​

    public bool Open()

    {

        isOpen = true;

        Console.WriteLine("Cello open for writing!");

        return isOpen;

    }

​

    public void Write(string text)

    {

        //write text if open

        if(isOpen)

            Console.WriteLine("Cello: " + text);

    }

}

​

class Parker : IPen

{

    public string Color { get; set; }

    private bool canWrite = false;

    public bool Close()

    {

        canWrite = false;

        Console.WriteLine("Parker is closed now!");

​

        return canWrite;

    }

​

    public bool Open()

    {

        canWrite = true;

        Console.WriteLine("Parker is open now!");

        return canWrite;

    }

​

    public void Write(string text)

    {

        //write text if open

        if(canWrite)

            Console.WriteLine("Parker: " + text);

    }

}

​

public class Program

{

    public static void Main()

    {

        IPen pen1 = new Cello();

        pen1.Open();

        pen1.Write("This is my Cello pen.");

        pen1.Close();

        IPen pen2 = new Parker();

        pen2.Open();

        pen2.Write("This is my Parker pen.");

        pen2.Close();

    }

}