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

dp=[0]*(1<<n)
for s in range(1<<n):
    for a in range(n):
        for b in range(a+1,n):
            if not(s>>a)&1: 
                if not(s>>b)&1:
                    dp[s|(1<<a)|(1<<b)]=max(dp[s|(1<<a)|(1<<b)],dp[s]+A[a]^A[b])

print(dp[(1<<n)-1])