using System;

public class unique

{

    static int a(int[] ar,int l)

    {

        int r=ar[0];

        for(int i=1;i<l;i++)

        r=r^ar[i];

        return r;

    }

    public static void Main()

    {

        int[] ar={2,3,4,5,3,4};

        int l=ar.Length;

        Console.WriteLine(a(ar,l));

    }

}