N = int(input())
A = list(map(int, input().split()))
dp = [0] * (1 << N)
for msk in range(1 << N):
    for i in range(N):
        if msk & 1 << i:
            continue
        for j in range(N):
            if msk & 1 << j:
                continue
            dp[msk | 1 << i | 1 << j] = max(dp[msk | 1 << i | 1 << j],
                                            dp[msk] + (A[i] ^ A[j]))
print(dp[-1])