using System;
using System.Collections.Generic;

class Program
{
    static void Main()
    {
        string[] words = Console.ReadLine().ToLower().Split(' ');

        var counts = new Dictionary<string, int>();

        foreach (var word in words)
        {
            if (counts.ContainsKey(word))
            {
                counts[word]++;
            }
            else
            {
                counts.Add(word, 1);
            }
        }

        var results = new List<string>();

        foreach (var pair in counts)
        {
            if (pair.Value % 2 != 0)
            {
                results.Add(pair.Key);
            }
        }
        Console.WriteLine(string.Join(", ", results));
    }
}