import sys
readline=sys.stdin.readline

N=int(readline())
A=list(map(int,readline().split()))
dp=[0]*(1<<N)
for bit in range(1<<N):
    lst=[i for i in range(N) if bit&1<<i]
    if len(lst)%2:
        continue
    l=len(lst)
    for j in range(l):
        for i in range(j):
            x,y=lst[i],lst[j]
            dp[bit]=max(dp[bit],dp[bit^1<<x^1<<y]+(A[x]^A[y]))
ans=dp[-1]
print(ans)