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

dp = [0] * (1 << N)
for S in range(1 << N):
    for i in range(N):
        if S & (1 << i):
            continue
        for j in range(i + 1, N):
            if S & (1 << j):
                continue
            dp[S | (1 << i) | (1 << j)] = max(
                dp[S | (1 << i) | (1 << j)], dp[S] + (A[i] ^ A[j])
            )
print(dp[-1])