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