using System;

namespace No246{
    public class Program{
        public static void Main(string[] args){
            Func<int, bool> q = x => {
                Console.WriteLine($"? {x}");
                return int.Parse(Console.ReadLine().Split(' ')[0]) == 0;
            };

            var left = 0;
            var right = 1000000001;

            while(left < right){
                var mid = (left + right) / 2;
                if(q(mid)){
                    right = mid;
                } else { 
                    left = mid + 1;
                }
            }

            Console.WriteLine(left - 1);
        }
    }
}