import java.util.*;

public class Main {
  public static void main(String[] args) {
    Scanner sc = new Scanner(System.in);
    int n = sc.nextInt();
    int p = 0;
    int l = 0;
    int r = (int)Math.pow(10, 9) + 1;
    int ans = 0;
    while(l < r) {
      int med = (l + r) / 2;
      System.out.println("? " + med);
      System.out.flush();
      int t = sc.nextInt();
      if(t == -1) {
        r = med - 1;
        p++;
      } else if(t == 1) {
        l = med;
        p++;
      } else {
        ans = med + p;
        System.out.println("! " + ans);
        System.out.flush();
        break;
      }
    }
  }
}