#include <iostream>
#include<stdio.h>

using namespace std;

int main() {
    int n, st, dr, mij, r;
    cin>>n;
    st=1;
    dr=n;
    while(st<=dr) {
       mij=(st+dr)/2;
       cout<<"?"<<mij<<endl;
       cin>>r;
       if(r==1 || r==-1) {
           dr=mij-1;
       }
       else {
        st=mij+1;
       }
    }
        cout<<"! "<<st<<endl;

    return 0;
}