#include <bits/stdc++.h>
using namespace std;
int st,dr,mid,r;
int main(){
    cin>>dr;
    st=1;
    while(st<=dr){
        mid=(st+dr)/2;
        cout<<"? "<<mid<<"\n";
        cout.flush();
        cin>>r;
        if(r==0)
            st=mid+1;
        else
            dr=mid-1;
    }
    cout<<"! "<<st<<"\n";
    cout.flush();
    return 0;
}