#include<iostream>
using namespace std;
int main()
{
    int st, dr, pp;
    cin>>dr;
    st = 1;
    int m = (st + dr) / 2;
    int rez;
    while(st<=dr)
    {
        m = (st + dr) / 2;
        cout<<"? "<<m<<endl;
        cin>>pp;
        if(pp == 0)
            st = m + 1;
        else if(pp == 1)
        {
            rez = m;
            dr = m - 1;
        }
        else
            return 0;
    }
    cout<<"! "<<rez<<endl;
    return 0;
}