How to disable close button on winForm?

using System.Runtime.InteropServices; //For "DllImportAttribute"

namespace Form1
{
    public partial class Form1 : Form
    {

        public Form1()
        {  
            InitializeComponent();
            CloseButton.EnableDisable(this, false);
}

     class CloseButton
        {
            private const int SC_CLOSE = 0xF060;
            private const int MF_GRAYED = 0x1;

            [DllImport("user32.dll")]
            private static extern IntPtr GetSystemMenu(IntPtr hWnd, bool bRevert);

            [DllImport("user32.dll")]
            private static extern int EnableMenuItem(IntPtr hMenu, int wIDEnableItem, int wEnable);

            public static void EnableDisable(Form form,bool isEnable)
            {
                EnableMenuItem(GetSystemMenu(form.Handle, isEnable), SC_CLOSE,  MF_GRAYED);
            }

        }
}