using System;

using System.Text.Json;

public class Program

{

    public static void Main()

    {

        var obj = new TestObj();

        obj.MyVal = 1234;

        obj.MyVal = 4567;

        var str = JsonSerializer.Serialize(obj);

        Console.WriteLine(str);

        Console.WriteLine("Hello World");

    }

    public class TestObj{

        public int MyVal;

        public int MyNewVal {get;set;}

    }

}