#!/usr/bin/env python3
import sys

def main():
    from itertools import combinations
    N = int(input())
    # N, K = map(int,input().split())
    A = list(map(int,input().split()))
    ans = 0
    for l in combinations(A, 2):
        ans = max(ans, l[0] ^ l[1])
    print(ans)

if __name__ == '__main__':
    main()