from collections import *
inf=10**16
n = int(input())
A = list(map(int,input().split()))
dp=[-inf]*(1<<n)
dp[0] = 0
for bit in range(1<<n):
    pre=dp[bit]
    for a in range(n):
        for b in range(a+1,n):
            if not (bit& (1<< a)) and  not (bit& (1<< b)):
                nbit = bit + (1 << a) + (1 << b)
                dp[nbit]=max(dp[nbit],dp[bit]+A[a] ^ A[b])

print(dp[-1])