using System;

using System.Linq;

using System.Collections.Generic;

​

public class Program

{

    public static void Main()

    {

        IList<int> numbers = new List<int> { 9,8,7,6,5,4,3,2,1};

        IEnumerable<int> results =

            numbers.OrderBy(x => x).Where((x, i) => i > 0 && (i + 1) % 3 == 0);

        foreach(var i in results)

        {

            Console.Write(String.Format("{0} ",i));

        }

    }

}