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

def dfs(mask, current_xor):
    if mask == (1 << N) - 1:
        return current_xor
    # Find the first unused player
    i = 0
    while i < N and (mask & (1 << i)):
        i += 1
    max_val = 0
    for j in range(i + 1, N):
        if not (mask & (1 << j)):
            new_mask = mask | (1 << i) | (1 << j)
            s = A[i] + A[j]
            res = dfs(new_mask, current_xor ^ s)
            if res > max_val:
                max_val = res
    return max_val

print(dfs(0, 0))