using System;
using static System.Console;
using System.Linq;
using System.Collections.Generic;
class Program
{
    static int NN => int.Parse(ReadLine());
    static int[] NList => ReadLine().Split().Select(int.Parse).ToArray();
    static int[] NMi => ReadLine().Split().Select(c => int.Parse(c) - 1).ToArray();
    static int[][] NMap(int n) => Enumerable.Repeat(0, n).Select(_ => NMi).ToArray();
    public static void Main()
    {
        Solve();
    }
    static void Solve()
    {
        var n = NN;
        for (var i = 0; i + 1 < n; i += 2)
        {
            WriteLine($"? {i} {i + 1}");
            var z = NN;
            if (z == i)
            {
                WriteLine($"! {i + 1}");
                return;
            }
            if (z == i + 1)
            {
                WriteLine($"! {i}");
                return;
            }
        }
        WriteLine($"! {n - 1}");
    }
}