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

dp = [0]*(1<<n)
for s in range(1<<n):
    p = 0
    for i in range(n):
        if (s>>i)&1:
            p += 1
    if p%2 == 1:
        continue
    for i in range(n-1):
        if (s>>i)&1:
            continue
        for j in range(i+1, n):
            if (s>>j)&1:
                continue
            dp[s|(1<<i)|(1<<j)] = max(dp[s|(1<<i)|(1<<j)], dp[s]+A[i]^A[j])
#print(dp)
print(dp[-1])