Hello.

As you already know the round was declared unrated. Firstly, we're extremely sorry that this happened and hope you enjoyed solving the problems regardless.

About what happened, the constraints for B were $$$t = 100$$$ and $$$n = 1000$$$ from the beginning i.e. for more than a month. This problem was supposed to be A initially, so I kept lower constraints than usual to ensure a small queue. At the same time, I didn't want trivial brutes to pass, so $$$n = 1000$$$ seemed like a good choice. Around 1 hour before the contest, a tester reminded me of his earlier feedback about increasing the number of test cases and adding a constraint on the sum of $$$n$$$, which would also make it more clear whether $$$\mathcal{O}(n^2)$$$ solutions should pass or not. At the same instant, I gave him WRITE access on polygon so that he could review all the problems.

Unfortunately, there was some miscommunication on my part leading him to think I have asked him to update the constraints. As a result, he updated the test data and the statement immediately, while I was busy doing last-minute checks. The problem was not intentionally updated during the round; he was under the impression that the contest starts $$$1$$$ hour later than it actually did because of a miscalculation due to Day Light Saving time in his country. As a result, a lot of people were solving problem for old constraints when in fact they were new while some also got RE.

Finally, please understand that this is an explanation of the events and not an excuse. I completely realize that such discussions should happen at least a day before the round, not an hour before. This was a result of many minor lapses, which all unluckily accumulated. I, Anton and, especially, the testers have put a lot of hard work into this round over the last $$$3$$$ months; the testers continuously pushed us to improve the quality of the contest through their honest feedback about the problems and overall difficulty, as well as improvements to the statements. Please do not blame them.

Once again, I am really sorry about this and hope you understand.