import sys
input=sys.stdin.readline
def I(): return int(input())
def MI(): return map(int, input().split())
def LI(): return list(map(int, input().split()))
mod=10**9+7

def main():
    N=I()
    A=LI()
    ans=0
    for i in range(N):
        for j in range(N):
            temp=A[i]^A[j]
            ans=max(ans,temp)
            
    print(ans)
    


main()