package brg.algo.cbinteractiv;

import java.util.Scanner;

public class Main {
    public static void main(String[] args) {
        Scanner sc = new Scanner(System.in);
        int l = 1;
        int r = sc.nextInt();
        while (l < r) {
            int mid = (l + r) / 2;
            System.out.println("? " + mid);
            int ans = sc.nextInt();
            if (ans == 0) {
                l = mid + 1;
            } else if (ans == 1) {
                r = mid;
            } else {
                return;
            }
        }
        System.out.println("! " + l);
        System.out.flush();
    }
}