#include<fstream>
#include<iostream>
#include<vector>
#include<cstring>
#include<algorithm>
using namespace std;

int n;

int main(){
  //ifstream cin("/usr/local/google/home/catavlas/ClionProjects/cf_training/subsecvente.in");
  ifstream cin("cbinteractiv.in");
  ofstream cout("cbinteractiv.out");

  cin>>n;
  int l = 1, r = n;
  while (l<=r) {
    int mid = (l+r)/2;
    cout<<"? "<<mid<<"\n";
    cout.flush();
    int x;
    cin>>x;
    if (x==-1) return 1;

    if (x==0) l = mid+1;
    else r = mid-1;
  }

  cout<<"! "<<l<<"\n";
  cout.flush();

  return 0;
}