n =int(input())
a = list(map(int,input().split()))

dp=[0]*(1<<n)

for i in range(1<<n):
    for j in range(n-1):
        for k in range(j+1,n):
            if  i >> j & 1 == 0 and i >> k & 1 == 0:
                dp[i|1<<j|1<<k] = max(dp[i|1<<j|1<<k],dp[i]+(a[j]^a[k]))

print(dp[- 1])