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

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

for mask in range(1<<n):
    for a in range(n):
        for b in range(a+1,n):
            if (1<<a)&mask == 0 and (1<<b)&mask == 0:
                dp[mask + ( 1<<a ) + (1<<b)] = max(dp[mask + (1<<a) + (1<< b)], dp[mask] + a_list[a]^a_list[b])
print(dp[(1<<n) -1])