using System;

public class Program

{

    public static void Main(string[] args)

    {

        int num = 20;

        Console.WriteLine(num);//1

        MyMethodIn(num);

        num++;

        Console.WriteLine(num);//5

    }

    public static void MyMethodIn(in int x)

    {

        int y = x;

        Console.WriteLine(y);//2

        y++;

        Console.WriteLine(y);//3

        Console.WriteLine(x);//4

    }

}

​