using System;

public class Program

{

    [Flags]

    public enum MyEnum : uint

    {

    None = 0,

    First = 1,

    Second= 2,

    Third= 4,

    Unknown = (uint)1 << 31, // Most-significant-bit.

    All = ~Unknown}

​

    public static void Main()

    {

        Console.WriteLine("All: " + ((uint)MyEnum.All).ToString("X"));

        Console.WriteLine("Unknown: " + ((uint)MyEnum.Unknown).ToString("X"));

    }

}