#include <iostream>

using namespace std;

int query(int X){
    cout << "? " << X << endl;

    int raspuns;
    cin >> raspuns;
    return raspuns;
}

int main()
{
    int n;

    cin >> n;

    int st = 1, dr = n, mij;

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

        if(query(mij) == 1){
            dr = mij - 1;
        }
        else{
            st = mij + 1;
        }
    }

    cout << "! " << st << endl;

    return 0;
}