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