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


def pop_count(T):
    T = (T & 0x55555555) + ((T >> 1) & 0x55555555)
    T = (T & 0x33333333) + ((T >> 2) & 0x33333333)
    T = (T & 0x0F0F0F0F) + ((T >> 4) & 0x0F0F0F0F)
    T = (T & 0x00FF00FF) + ((T >> 8) & 0x00FF00FF)
    T = (T & 0x0000FFFF) + ((T >> 16) & 0x0000FFFF)
    return T


dp = [0] * (1 << N)
for S in range(1 << N):
    if pop_count(S) % 2 == 1:
        continue
    for i in range(N - 1):
        if ~(S >> i) & 1:
            for j in range(i + 1, N):
                if ~(S >> j) & 1:
                    U = S ^ (1 << i) ^ (1 << j)
                    if dp[U] < dp[S] + (A[i] ^ A[j]):
                        dp[U] = dp[S] + (A[i] ^ A[j])
print(dp[(1 << N)-1])