#include <iostream>

using namespace std;

int main()
{
    int n;
    cin>>n;
    int st=1,dr=n,rez=0;
    while(st<=dr){
        int mij=(st+dr)/2;
        cout << "? " << mij << flush;
        int rasp;
        cin>>rasp;
        if(rasp==0){
            st=mij+1;
            rez=mij;
        }else{
            dr=mij-1;
        }
    }
    cout<<"! "<<st<<"\n"<<flush;
    return 0;
}