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

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