import java.util.*;
public class Main {

  public static int parse(String s) {
    int n = 0;
    for(int i = 0; i < s.length(); i++)
      n = n * 10 + s.charAt(i) - '0';
    return n;
  }

  public static void main(String[] args)  {
    Scanner in = new Scanner(System.in) ;
    int n = parse(in.next());
    
    int from = 1, to = n;
    while(from < to) {
      int mid = (from + to) / 2;
      System.out.print("? ");
      System.out.println(mid);
      System.out.flush();
      String s; s = in.next();
      if (s.equals("1"))
        to = mid;
      else
        from = mid + 1;
    }

    System.out.print("! ");
    System.out.println(from);
    System.out.flush();
  }
}