N = int(input())
A = list(map(int,input().split()))
dp = [0]*(1<<N)

for i in range(1<<N):

    
    for s in range(N-1):
        for t in range(s+1,N):
            tmp = (1<<s)|(1<<t)
    
            if i&tmp:
                continue
            else:
                dp[i|tmp] = max(dp[i|tmp],dp[i] + (A[s]^A[t]))
            
print(dp[-1])