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

dp = [-1]*(1<<N)
dp[0] = 0
for i in range(1<<N):
    for j in range(N):
        for k in range(j+1, N):
            if i&(1<<j)==0 and i&(1<<k)==0 and dp[i]>=0:
                dp[i+(1<<j)+(1<<k)] = max(dp[i+(1<<j)+(1<<k)], dp[i] + (A[j]^A[k]))
print(dp[-1])