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

DP = [0 for _ in range(1 << n)]
for bit in range(1, 1 << n):
    L = []
    for i in range(n):
        if (bit >> i) & 1:
            L.append(i)
    if len(L) % 2 == 1:
        continue
    if len(L) == 2:
        i, j = L[0], L[1]
        DP[bit] = A[i] ^ A[j]
    else:
        for x in range(len(L)):
            for y in range(x + 1, len(L)):
                i, j = L[x], L[y]
                rbit = (1 << i) + (1 << j)
                DP[bit] = max(DP[bit], DP[bit - rbit] + (A[i] ^ A[j]))
print(DP[-1])