using System;

public class Program

{

    public static void Main()

    {

        var data = new Data(10);

        var first = new First(data);

        var second = new Second(data);

        second.Multiply(5);

        first.Add(10);

        Console.WriteLine("Data value is {0}",data.Value);

    }

}

​

public class Data{

    public Data(int value)

    {

        this.Value = value;

    }

    public int Value{get;set;}

}

​

public class First{

    private Data m_data;

    public First(Data data)

    {

        m_data = data;

    }

    public void Add(int value)

    {

        if(m_data!=null)

            m_data.Value+=value;

    }

}

​

public class Second{

    private Data m_data;

    public Second(Data data)

    {

        m_data = data;

    }

    public void Multiply(int value)

    {

        if(m_data!=null)

            m_data.Value*=value;

    }

}