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

dp = [0]*(1<<N)
for msk in range(1<<N):
    for i in range(N-1):
        if msk & (1<<i) != 0:
            continue
        for j in range(i+1, N):
            if msk & (1<<j) != 0:
                continue                
            dp[msk+(1<<i)+(1<<j)] = \
                max(dp[msk+(1<<i)+(1<<j)], dp[msk] + (A[i] ^ A[j]))
ans = dp[(1<<N)-1]
print(ans)