using System;

​

public class Program

{

    public static void Main()

    {

        var car = new Car();

        car.IncreaseSpeed();

        car.IncreaseSpeed();

        car.IncreaseSpeed();

        car.IncreaseSpeed();

        car.IncreaseSpeed();

    }

}

​

public class Car

{

    private readonly Gearbox _gearbox;

    private readonly Engine _engine;

    public Car()

    {

        _gearbox = new Gearbox();

        _engine = new Engine();

    }

​

    public virtual void IncreaseSpeed()

    {

        if (_engine.Rpm >= 4000)

        {

            _gearbox.ChangeUp();

        }

​

        _engine.IncreaseSpeed();

    }

}

​

public class Gearbox

{

    public int CurrentGear

    {

        get;

        internal set;

    }

​

    public void ChangeUp()

    {

        Console.WriteLine($"Gearbox changed up");

    }

}

​

public class Engine

{

    public virtual int Rpm

    {

        get;

        set;

    }

​

    public virtual void IncreaseSpeed()

    {

        Rpm = Rpm + 1000;

        Console.WriteLine($"Engine increased speed Rpm:{Rpm}");

    }

}