#include <iostream>
using namespace std;

int main() {
    int N;
    cin >> N;

    int left = 1, right = N;
    while (left <= right) {
        int mid = left + (right - left) / 2;
        cout << "? " << mid << endl;
        cout.flush();

        int response;
        cin >> response;

        if (response == 0) {
            cout << "! " << mid << endl;
            cout.flush();
            break;
        } else if (response == 1) {
            left = mid + 1;
        } else if (response == -1) {
            right = mid - 1;
        }
    }

    return 0;
}