using System;

public class Program
{
	public static void Main()
	{
		int min = 0, max = (int)Math.Pow(10, 9);
		int mid;
		for (mid = (min + max) / 2; min != max; mid = (min + max) / 2)
		{
			Console.WriteLine("? {0}", mid);
			bool isLess = int.Parse(Console.ReadLine()) == 0;
			if (isLess)
			{
				max = mid - 1;
			}
			else
			{
				min = mid;
			}
		}
		Console.WriteLine(mid);
	}
}