#include <iostream>
using namespace std;

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

        mij=(dr+st)/2;
        cout<<"? "<<mij<<'\n';
        cout.flush();
        cin>>answ;
    }
    cout<<"! "<<dr;
}