# yukicoder No.698 ペアでチームを作ろう
# 解答閲覧


def main():

    N = int(input())

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

    dp = [0]*(2**N+10)
    for n in range(1<<N):
        for i in range(N):
            for j in range(i+1,N):
                if (n & (1<<i)):
                    continue
                if (n & (1 <<j)):
                    continue
                dp[n + 2**i + 2**j] = max(dp[n+2**i+2**j], dp[n] + (A[i]^A[j]))

    
    print(dp[2**N-1])


if __name__ == '__main__':
     main()