N = int(input())
A = list(map(int, input().split()))
N2 = 1 << N
inf = 10 ** 18
dp = [-inf] * N2
dp[0] = 0
for s in range(N2):
    for a in range(N):
        for b in range(a + 1, N):
            if (s >> a) & 1:
                continue
            if (s >> b) & 1:
                continue
            ns = s | (1 << a) | (1 << b)
            dp[ns] = max(dp[ns], dp[s] + (A[a] ^ A[b]))
print(dp[-1])