#include <iostream>

using namespace std;

int main(){
    int st, dr, mid, sol;
    bool ans;

    st = 1;
    cin >> dr;

    sol = dr;
    while(st <= dr){
        mid = (st + dr) / 2;

        cout << "? " << mid << endl;
        cin >> ans;

        if(ans){
            sol = mid;
            dr = mid - 1;
        }
        else{
            st = mid + 1;
        }
    }

    cout << "! " << sol << endl;

    return 0;
}