using System;

using System.Collections;

​

public class Program

{

    public static void Main()

    {

        Console.WriteLine("Hello World");

        int[] a = Array.ConvertAll<string, int>(Console.ReadLine().Split(' '), int.Parse);

        Hashtable hs = new Hashtable();

        Array.ForEach(a, i =>

        {

            if (!hs.ContainsKey(i))

            {

                hs.Add(i,1);

            }

            else{

             hs.Remove(i);

            }

        });

        foreach(int keys in hs.Keys){

        Console.WriteLine(keys);

        }

    }

}

///2 2 4 4 6 6 7 7 5