Как отправить выбранные значения listbox из одного listbox в другой в ASP.NET MVC без использования клиентского кода

I want to send selected listbox values to another listbox. I want to implement this using C# code in controller section but not with JavaScript code.

I got stuck here. I am generating integer values and want to select these values to send to another list box and vice-versa.

public class NumberClass
  {
    public IEnumerable<SelectListItem> leftnumbers { get; set; }
    public IEnumerable<int> leftSelectednumbers { get; set; }

    public IEnumerable<SelectListItem> rightnumbers { get; set; }
    public IEnumerable<int> rightSelectednumbers { get; set; }
  }

[HttpGet]
      public ActionResult Index()
      {
        List<SelectListItem> items = new List<SelectListItem>();

        for (int i = 1; i <= 20; i++)
        {
            SelectListItem selectList = new SelectListItem()
            {
                Text = i.ToString(),
                Value = i.ToString()

            };

            items.Add(selectList);

        }

        NumberClass num = new NumberClass()
        {
            leftnumbers = items,
            rightnumbers = null

        };
        return View(num);

    }


    [HttpPost]
    public string Index(IEnumerable<int> selectedvalue)
    {
        if (selectedvalue == null)
        {
            return "you have not selected";
        }
        else
        {
            //
            return;
        }

    }

@using (Html.BeginForm())
{
  <div class="col-md-6" style="font-family:Arial">
    @Html.ListBoxFor(m => m.leftSelectednumbers, Model.leftnumbers, new { size = 20, @class = "listBox" })
    <br />
    <input type="submit" value="move left" />
</div>

<div class="col-md-6" style="font-family:Arial">

    @Html.ListBoxFor(m => m.leftSelectednumbers, new List<SelectListItem>(), new { size = 20, @class = "listBox" })
    <br />
    <input type="submit" value="move right" />
</div>

}