#include <iostream>
using namespace std;
int n,st,dr,mij,ok;
int main()
{
    cin>>n;
    st=1;
    dr=n;
    while (st<=dr)
    {
        mij=(st+dr)/2;
        cout<<"? "<<mij<<"\n";
        cout.flush ();
        cin>>ok;
        if (ok==-1)
            exit (0);
        if (ok==1)
            dr=mij-1;
        if (ok==0)
            st=mij+1;
    }
    cout<<"! "<<st<<"\n";
    cout.flush ();
    return 0;
}