from collections import *
from itertools import *
from functools import *
from heapq import *
import sys,math

N = int(input())
A = list(map(int,input().split()))
ans = 0
for i in range(N-1):
    ai = A[i]
    for j in range(i+1,N):
        aj = A[j]
        ans = max(ans,ai^aj)
print(ans)