public class OuterClass

{

    internal OuterClass()

    {

        System.Console.WriteLine("OuterClass");     

    }

​

    private class NestedClass

    {

        public NestedClass()

        {

            System.Console.WriteLine("NestedClass");     

        }

        internal class Secret

        {

            Secret()

            {

            }

        }

    }

}

​

public class Demo : OuterClass

{

    public static void Main()

    {

        Demo dc = new Demo();    

        System.Console.WriteLine("Demo");

    }

}