N = int(input())
A = list(map(int, input().split()))


dp = [0] * (1 << N)

for S in range(1 << N):
    for u in range(N):
        if S & (1 << u):
            continue
        for v in range(u+1, N):
            if S & (1 << v):
                continue
            dp[S | (1 << u) | (1 << v)] = max(dp[S | (1 << u) | (1 << v)], dp[S] + (A[u] ^ A[v]))

# print(dp)
print(dp[-1])