using System;
using System.Collections.Generic;
using System.Linq;
using System.Text;
using System.Threading.Tasks;

namespace ArrayExercise
{
    class Program
    {
        static void Main(string[] args)
        {
            var words = Console.ReadLine().ToLower().Split(' ');
            var allWords = new Dictionary<string, int>();
            foreach (var word in words)
                if (!allWords.ContainsKey(word))

                    allWords.Add(word, 1);
                else
                    allWords[word]++;
            var result = new List<string>();
            foreach (var pair in allWords)
            {
                if (pair.Value % 2 == 1)
                {
                    result.Add(pair.Key);
                }
            }
            Console.WriteLine(string.Join(", ", result));
        }
    }
}