Really Dynamic Master Pages

using System;
using System.Collections.Generic;
using System.Linq;
using System.Web;
using System.Web.UI;
using System.Web.UI.WebControls;

namespace DynamicMasterPages
{
    public partial class MasterPage2 : System.Web.UI.MasterPage
    {
        int num;

        public MasterPage2()
        {
            object cphnum = HttpContext.Current.Session["cphnum"];
            if (cphnum == null || !(cphnum is int))
                return;
            num = (int)cphnum;
            //create the contentplaceholders to be paired with the content
            for (int i = 1; i < num + 1; i++)
                base.ContentPlaceHolders.Add("contentplaceholder" + i.ToString());
        }

        protected void Page_Init(object sender, EventArgs e)
        {
            if (num == 0)
                return;
            Literal b = new Literal();
            b.ID = "Literal1";
            b.Text = "Master";
            PlaceHolder1.Controls.Add(b);
            for (int i = 1; i < num + 1; i++)
            {
                ContentPlaceHolder cph = new ContentPlaceHolder();
                cph.ID = "ContentPlaceHolder" + i.ToString();
                PlaceHolder1.Controls.Add(cph);
                if (base.ContentTemplates != null)
                {
                    //fill the content placeholders with content from content page
                    //will throw NullReferenceException if content does not exist
                    ((ITemplate)base.ContentTemplates["ContentPlaceHolder" + i.ToString()]).InstantiateIn(cph);
                }
            }
        }
    }
}