N = int(input())
A = list(map(int, input().split()))
dp = [0 for _ in range(2 ** N)]

for msk in range(0, 2 ** N):
    for a in range(N):
        for b in range(a+1, N):
            if not(msk & (1<<a)):
                if not(msk & (1<<b)):
                    dp[msk + (1 << a) + (1 << b)] = max(dp[msk + (1 << a) + (1 << b)], dp[msk] + (A[a] ^ A[b]))
print(dp[-1])