def main():
    N = int(input())
    A = list(map(int,input().split()))
    dp = [0]*(1<<N)
    for s in range(0, 1<<N):#集合を添字の小さい順に試す
        for i in range(N):#全ての要素のペアを考える
            for j in range(i+1,N):
                if ((s>>i)&1)==0 and ((s>>j)&1)==0:#i in not s and j in not s
                    if dp[s+(1<<i)+(1<<j)]<dp[s]+(A[i]^A[j]):
                        dp[s+(1<<i)+(1<<j)]=dp[s]+(A[i]^A[j])
    return dp[-1]
print(main())