package com.radu;

import java.util.Scanner;

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

        int response = in.nextInt();
        if(response == 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);
        int n = in.nextInt();
        System.out.println("! " + binarySearch(in, 1, n));
        System.out.flush();
    }
}