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

dp = [0]*(1 << N)
for i in range(1 << N):
    for a in range(N):
        for b in range(N):
            if a == b:
                continue
            if (i >> a) & 1:
                continue
            if (i >> b) & 1:
                continue
            dp[i | (1 << a) | (1 << b)] = max(dp[i | (1 << a) | (1 << b)], dp[i] + (A[a] ^ A[b]))

print(dp[-1])