#include <iostream>

using namespace std;

int main() {
    int n;
    cin >> n;
    int st = 1, dr = n;
    while (st < dr) {
        int m = (st + dr) / 2, tmp;
        cout << "? " << m << "\n";
        cout.flush();
        cin >> tmp;
        if (tmp == 0)
            st = m + 1;
        else
            dr = m;
    }
    cout << "! " << st << "\n";
    cout.flush();
    return 0;
}