N=int(input())
A=list(map(int,input().split()))
MAX=1<<N
dp=[0 for _ in range(MAX)]
for s in range(MAX):
    for i in range(N):
        for j in range(i+1,N):
            if (s>>i)&1==0 or (s>>j)&1==0:continue
            bs=s
            bs^=1<<i
            bs^=1<<j
            dp[s]=max(dp[s],dp[bs]+(A[i]^A[j]))
print(dp[-1])