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 x = 0;

    for (int jump = (1 << 30); 0 < jump; jump /= 2) {
      if(x + jump <= n) {
        x += jump;
        System.out.print("? ");
        System.out.println(x);
        System.out.flush();
        String s; s = in.next();
        if (s.equals("1"))
          x -= jump;
      }
    }

    System.out.print("! ");
    System.out.println(x + 1);
    System.out.flush();
  }
}