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