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