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

bit_count = lambda b: bin(b).count("1")

dp = [0] * (1 << N)
for b in range(1 << N):
    if bit_count(b) % 2:
        continue
    for i in range(N):
        if (b >> i) & 1:
            continue
        for j in range(i + 1, N):
            if (b >> j) & 1:
                continue
            c = b | (1 << i) | (1 << j)
            dp[c] = max(dp[c], dp[b] + (A[i] ^ A[j]))
print(dp[-1])