import java.util.Scanner;

import static java.lang.System.out;

public class Main {
    public static void main(String[] args) {
        Scanner sc = new Scanner(System.in);
        int left = 1;
        int right = sc.nextInt();
        while (left < right) {
            int half = (left + right) / 2;
            out.println("? " + half);
            switch (sc.nextInt()) {
                case 0 -> left = half + 1;
                case 1 -> right = half;
                default -> {
                    return;
                }
            }
        }
        out.println("! " + left);
        out.flush();
    }
}