int andXorOr(int N, const vector<int>& A) {
    int maxXOR = 0;
    vector<int> prevSmaller(N, -1), nextSmaller(N, N);
    stack<int> prev, next;
    prev.push(0);
    next.push(N - 1);
    for (int i = 1; i < N; i++) {
        while (!prev.empty() and A[prev.top()] >= A[i]) prev.pop();
        if (!prev.empty()) prevSmaller[i] = prev.top();
        prev.push(i);
    }
    for (int i = N - 2; i >= 0; i--) {
        while (!next.empty() and A[i] <= A[next.top()]) next.pop();
        if (!next.empty()) nextSmaller[i] = next.top();
        next.push(i);
    }
    for (int i = 0; i < N; i++) {
        if (prevSmaller[i] != -1) maxXOR = max(maxXOR, A[i] ^ A[prevSmaller[i]]);
        if (nextSmaller[i] != N) maxXOR = max(maxXOR, A[i] ^ A[nextSmaller[i]]);
    }
    return maxXOR;
}