using System;

namespace Vetélked
{
    class Program
    {
        static void Main(string[] args)
        {
            int count = int.Parse(Console.ReadLine());
            int[] karakterek = new int[20];
            for (int i = 0; i < count; i++)
            {
                foreach (char u in Console.ReadLine())
                {
                    karakterek[u] ^= 1;
                }
            }
            for (int i = 0; i < 20; ++i)
            {
                if (karakterek[i] == 1)
                {
                    Console.Write((char)i);
                }
            }
        }
    }
}