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

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

def popcnt(x):
    res = 0
    while x:
        res += (x & 1)
        x >>= 1
    return res
    
for status in range(1 << N):
    if popcnt(status) & 1:
        continue
    for i in range(N):
        if (status >> i) & 1:
            continue
        for j in range(i + 1, N):
            if (status >> j) & 1:
                continue
            next_status = status | (1 << i) | (1 << j)
            dp[next_status] = max(dp[next_status], dp[status] + (A[i] ^ A[j]))
            
print(dp[-1])