I can't figure out a way to unblock 1713D - Отсчет турнира. I used some wrappers over Console for easier testing, but even with pure Console usage it gets stuck on test 3: 167411234.

I do:

Console.WriteLine("? 1 2");
Console.Out.Flush();

And perform all reads by Console.ReadLine() only.

What can be the reason for this?