import java.util.Scanner;

public class Main {
    public static long binarySearch(Scanner in, long left, long right) {
        if (left >= right) return left;
        long mid = (right - left) / 2 + left;
        System.out.print("? ");
        System.out.println(mid);
        System.out.flush();

        String response = in.next();
        if (response.equals("0")) {
            return binarySearch(in, mid + 1, right);
        } else {
            return binarySearch(in, left, mid);
        }
    }

    public static void main(String[] args) {
        Scanner in = new Scanner(System.in);
        long n = in.nextInt();
        System.out.print("! ");
        System.out.println(binarySearch(in, 1, n));
        System.out.flush();
    }
}