using System;
using System.Collections.Generic;

class OddOccurance
{
    static void Main()
    {
        var words = Console.ReadLine().ToLower().Split(' ');
        var result = new List<string>();

        var allWords = new Dictionary<string, int>();
        foreach (var word in words)
        {
            if (!allWords.ContainsKey(word))
            {
                allWords.Add(word, 1);
            }
            else
            {
                allWords[word]++;
            }
        }

        foreach (var item in allWords)
        {
            if (item.Value % 2 == 1)
            {
                result.Add(item.Key);
            }
        }

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