using System;

using System.Linq;

public class Program

{

    public static void Main()

    {

        int[] a = new int[]{ 1, 3, 5, 7, 9 };

        int[] b = new int[]{ 1, 5, 9, 11 };

        // Get the items in a that are not in b

        var result = a.Intersect(b); // yields { 1, 5, 9 }

        Console.WriteLine(String.Join(",",result.ToArray()));

    }

}