using System;
using static System.Console;
using System.Linq;
using System.Collections.Generic;

class Program
{
    static int NN => int.Parse(ReadLine());
    static long[] NList => ReadLine().Split().Select(long.Parse).ToArray();
    public static void Main()
    {
        Solve();
    }
    static void Solve()
    {
        var n = NN;
        var a = NList;
        for (var i = 0; i < 63; ++i)
        {
            var x = 1L << i;
            var flg = true;
            foreach (var ai in a) if (x + ai != (x ^ ai)) flg = false;
            if (flg)
            {
                WriteLine(x);
                return;
            }
        }
    }
}