using System;

using System.Collections.Generic;

public class Program

{

    //Obtain number of non repeated chars

    public static void Main()

    {

        var str = "acdeeabcad";

        var result = FindNonRepeated(str);

        Console.WriteLine(result.Count);

        foreach (var letter in result) {

            Console.Write($"{letter},");

        }

    }

    private static HashSet<char> FindNonRepeated(string str) {      

        var hsNonRepeated = new HashSet<char>();

        var hsRepeated = new HashSet<char>();

        for (var i = 0; i < str.Length; i++){

            var letter = str[i];

            if (!hsNonRepeated.Contains(letter) && !hsRepeated.Contains(letter)){

                hsNonRepeated.Add(letter);              

            }

            else{

                hsNonRepeated.Remove(letter);

                hsRepeated.Add(letter);             

            }

        }

        return hsNonRepeated;

    }

}