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

dp = [0] * (2**N)
for bit in range(2**N):
    rest = []
    for i in range(N):
        if (bit >> i) & 1:
            continue
        rest.append(i)
    if len(rest) % 2:
        continue

    for i, j in combinations(rest, 2):
        dp[bit|1<<i|1<<j] = max(dp[bit|1<<i|1<<j], dp[bit]+(A[i]^A[j]))

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