# X = B1^B2^---^Bn-1 = A1^A2^A2^A3^----^An-1^An-1^An = A1^An
# つまり間の項は全部打ち消しあい、A1^Anだけが残る、その最大値が答え

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