using System;

using System.Linq;

public class Program

{

    public static void Main()

    {

        var input = new string[] {"A","A","B","B","B","C","D","E","E","F"};

        var result = input.GroupBy(x => x).Where(x => x.Count() == 1).Select(x => x.Key).ToList();

        Console.WriteLine(string.Join(",",result));

    }

}