#include <bits/stdc++.h>
using namespace std;

int n;

int main() {
    int rv;
    cin >> n;
    cout.flush();
    int st = 1, dr = n;
    while (st < dr) {
        int mid = st + (dr - st) / 2;
        cout << "? " << mid << "\n";
        ///_sleep(3000);
        cout.flush();
        cin >> rv;
        ///_sleep(3000);
        if (rv == 1) {
            dr = mid;
        }
        else st = mid + 1;
    }
    cout << "! " << st ;
}