using System;
using static System.Console;
using System.Linq;
using System.Collections.Generic;

class Program
{
    static int NN => int.Parse(ReadLine());
    static long[] NList => ReadLine().Split().Select(long.Parse).ToArray();
    public static void Main()
    {
        Solve();
    }
    static void Solve()
    {
        var prime = Enumerable.Repeat(true, 1014).ToArray();
        prime[0] = false;
        prime[1] = false;
        var plist = new List<int>();
        for (var i = 2; i < prime.Length; ++i) if (prime[i])
        {
            plist.Add(i);
            for (var j = i * 2; j < prime.Length; j += i) prime[j] = false;
        }
        if (!IsSafe(2))
        {
            WriteLine(IsSafe(1) ? "! 1" : "! 0");
            return;
        }
        var ok = 0;
        var ng = plist.Count;
        while (ng - ok > 1)
        {
            var mid = (ok + ng) / 2;
            if (IsSafe(plist[mid])) ok = mid;
            else
            {
                if (IsSafe(plist[mid + 1]))
                {
                    var ok2 = mid + 1;
                    while (ng - ok2 > 1)
                    {
                        var mid2 = (ok2 + ng) / 2;
                        if (IsSafe(plist[mid2])) ok2 = mid2;
                        else ng = mid2;
                    }
                    break;
                }
                else ng = mid;
            }
        }
        if (IsSafe(plist[ng] + 1))
        {
            ok = plist[ng] + 1;
            ng = plist[ng + 1];
            while (ng - ok > 1)
            {
                var mid = (ok + ng) / 2;
                if (IsSafe(mid)) ok = mid;
                else ng = mid;
            }
            WriteLine("! " + ok);
        }
        else
        {
            ok = plist[ng - 1];
            ng = plist[ng];
            while (ng - ok > 1)
            {
                var mid = (ok + ng) / 2;
                if (IsSafe(mid)) ok = mid;
                else ng = mid;
            }
            WriteLine("! " + ok);
        }
    }
    static bool IsSafe(int n)
    {
        WriteLine($"? {n}");
        return ReadLine() == "safe";
    }
}