import sys
def input():
    return sys.stdin.readline()[:-1]
def main():
    MOD = 10**9 + 7
    N = int(input())
    A = list(map(int,input().split()))
    ans = 0
    for i in range(N-1):
        for j in range(i+1,N):
            ans = max(ans,A[i]^A[j])
    print(ans)
if __name__ == '__main__':
    main()