using System;

public class Program

{

    public static void Main()

    {

        var a = new A();

        Console.WriteLine(a.x);

        a.f();

        Console.WriteLine(a.x);

    }

}

​

​

​

class B

{

    public B() {}

​

    public void h(Action a)

    {

        a();

    }

}

​

class A

{

    public int x = 0;

    private void g()

    {

        x = 5;

    }

​

    public void f()

    {

        B b = new B();

        b.h(g);

    }

}