import java.io.*;
import java.util.*;
import java.util.function.*;
import java.util.stream.*;

public class Main {
    public static void main(String[] args) throws Exception {
        Scanner sc = new Scanner();
        int n = sc.nextInt();
        for (int i = 0; i < n; i += 2) {
            System.out.println("? " + i + " " + (i + 1));
            System.out.flush();
            int x = sc.nextInt();
            if (x == i) {
                System.out.println("! " + (i + 1));
                System.out.flush();
                return;
            } else if (x == i + 1) {
                System.out.println("! " + i);
                System.out.flush();
                return;
            }
        }
        System.out.println("! " + (n - 1));
        System.out.flush();
    }
}
class Scanner {
    BufferedReader br;
    StringTokenizer st = new StringTokenizer("");
    StringBuilder sb = new StringBuilder();
    
    public Scanner() {
        try {
            br = new BufferedReader(new InputStreamReader(System.in));
        } catch (Exception e) {
            
        }
    }
    
    public int nextInt() {
        return Integer.parseInt(next());
    }
    
    public long nextLong() {
        return Long.parseLong(next());
    }
    
    public double nextDouble() {
        return Double.parseDouble(next());
    }
    
    public String next() {
        try {
            while (!st.hasMoreTokens()) {
                st = new StringTokenizer(br.readLine());
            }
        } catch (Exception e) {
            e.printStackTrace();
        } finally {
            return st.nextToken();
        }
    }
    
}