#include <iostream>

using namespace std;

int dr, st, op;

int main() {
    cin >> dr;
    st = 1;
    while(st <= dr) {
        int mid = (st + dr) >> 1;
        cout << "?" << " " << mid << '\n';
        cout.flush();
        cin >> op;
        if(op == 0)
            st = mid + 1;
        else dr = mid - 1;
    }

    cout << dr;
    cout.flush();

    return 0;
}