#include <bits/stdc++.h>
using namespace std;

int query (int X){
  cout<<"? "<<X<<endl;
  int res;
  cin>>res;
  return res;
}

int main()
{
    int n;
    in>>n;
    int st=1 , dr=n;
    while(st<=dr){
      int mid=(st+dr)/2;
      if(query(mid) == 1){
        dr=mid-1;
      }
      else{
        st=mid+1;
      }
    }
    cout<<"! "<<st<<endl;
    return 0;
}