import itertools
N = int(input())
A = list(map(int,input().split()))

dp = [0]*(1<<N)

for s in range(1<<N):
    for i,j in itertools.combinations(range(N),2):
        if not s&(1<<i) and not s&(1<<j):
            dp[s|(1<<i)|(1<<j)] = max(dp[s|(1<<i)|(1<<j)], dp[s]+(A[i]^A[j]))

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