#include <iostream>

using namespace std;

int main()
{
    int n, st, dr;
    cin >> n;
    st = 1;
    dr = n;
    while (st < dr)
    {
        int x = (st + dr) / 2;
        cout << "? " << x << endl;
        int raspuns;
        cin >> raspuns;
        if (raspuns == -1)
        {
            return 0;
        }
        if (raspuns == 0)
        {
            st = x + 1;
        }
        else
        {
            dr = x;
        }
    }
    cout << "! " << st << endl;
    return 0;
}