Literally, 1937C - Bitwise Operation Wizard is the best one I've ever seen.

Oh, subtask in problem B! It must be interesting!

Oh, you think G2 and G3 aren't good problems... Then why they are in contest? Isn't it wierd? Is it OK that not good problems in Div.4?

But educational problems should not affect rating.

Then why Educational CodeForces (Div.2) exists? Just do plug all Educational CodeForces problem in Div.3 or Div.4. But there is reason that Educational CodeForces exists.

And why you're saying like that? Nobody said "I want to solve all of them!"

I'm just saying that problem must be its suitable position, so it can teach more people. If you do not think so, then I'm sorry. But I believe every problemsetter and coordinator, tester knows that Div.4 is not for Master or Grandmaster, but for Newbie or Pupil.

Why Div.4 have to educate Master or Grandmaster? I cannot understand.

I think that that an overwhelmingly difficult problem is standard so can't put it in Div.2 doesn't mean that it can plugged in Div.4. I want a good problem must to be placed where a more people can solve it.

I love E, F, G2. Brilliant idea!!!

In NEAR, orange is yellow!

Erm... That is Div.2 only, and participants are ~2099. You have to read again my comments.

The point is *2100 is not suitable for ~1399, *2600 is not suitable for ~1899. (That's what I said before!)

And yes, also in this case, E2 is not suitable for this range of participants(note that I did not said that task is no use or quality is low or no good! Just good task missed for its seat.). Actually only 9 rated participants solved E2.

It would be better that range of rated participants are ~2399 for *2700 and *3100 last two tasks(or unlimited), but I save my words because I have no authority to adjust range of rated participants.

Plus) I can't get rid of the impression that you choose your words wierd. In your link, who solved E2 and F are not fake at all. They just got a low rating compared to their level. They will probably go up. That's it.

Also I had some 2600 being solved (alright, not in contest) while being in 1600-1899 range. Which means it gives chance of one in thousand to solve it.

That's what exactly what I said. Even you, now are CM, cannot solved *2600 during the contest. That is what I afraid, very good task goes to archive, and waiting someone.

Contest, again, stands for rated participants, and solvability during the contest is important. Even me, given plenty of time and my target is in my speciality zone, can solve one of the hardest one in Petrozavodsk Camp. So I would ask you not to misrepresent my intentions: it would be a waste to have a task that no one can solve, and I don't want to solve easy problems just for the sake of it, either.

Umm... do you really think existense of *2500 or harder task matter the comfort zone of 1600~1899? I think not. You should missed the point... The point is *2100 is not suitable for ~1399, *2600 is not suitable for ~1899. The comfort zone doesnt matter.

Adding extremely hard task that 99.99% of rated participants cannot solve is meaningless, because only chosen 1% or less try that task in contest time and finally that buried in archive. This is no good. This is all I want to say.

Or you just want to say *3100 D2F is OK. But I don't think so.

Contest is stands for rated participants, I think. If not, then what I'm about to say is just.., yes. Kind of nonsense.

I'm not advocating that problemsetter must just lower the difficulty. I'm saying that it's necessary to moderate the difficulty for the people who will be solve them.

(Not Div.2 only.) Div.2, with Div.1 considers only those with a rating of 1899 or less to be rated participants. This means that very few people can solve *2500 or higher during the competition.

It was my mistake to mislead by using an extreme example and not explaining it. *800 *1100 *1400 *1700 *2100 *2500 like contest would be better then examples I gave before. However, I think need to consider what kind of rated partipants will be solving this task during the competition.

If a *2100 task is too standard to be in Div.2 or Div.1, why not put it in Educational CodeForces instead of Div.4? Why does Div.2 with Div.1, have to obey the formula D2F=D1D? I believe contest divisions could be improvable and give everyone more satisfaction.

*800 *1000 *1300 *1600 *1900 *2100 is more true for div2 than *800 *1300 *1700 *2100 *2500 *3000. Div2 is rated for ~1899, and no 1899 can solve *3000(except for future GM).

Difficult div2 often feels like div1.5, which may be good for M or CM, but is disastrous for E. Creating difficult well-made task is very difficult, and I think it is impossible for the rated participants of div2 to solve *2500 or harder task. Why not save the most difficult task for div1? Wouldn't it be satisfactory for everyone if put in a moderately easy problem(yes, around *1000~*1500) instead?

Regardless of the high or low, I think rating after solving 4 or more tasks is more true than solving 2 or less. The latter tends to be more easily fluctuated by luck than the former.

This is a huge insult. I'm sure I'm not the only one who agrees with.

I don't know if I'm qualified to say this, but can't you be kind to other? Can't you at least be kind enough to not be sarcastic or insult someone who has nothing to do with you and has raised a legitimate issue?

Who on earth gave this guy the wrong info saying it's OK to be rude if you're CM?

Thanks for your brilliant problems! Round was fun enough to spend full competition time just solving the problem.

I hope everyone have a great time with this Div.3!!!

And I wish my positive delta. I'm 1599 now...

Nope, never. Regardless of the difficulty of the question, plagiarism is a serious issue.

Very long time no see, Educational Codeforces. I wish this contest teach me a lot.

As a personal review by cyan-blue contestant participating Div2:

==

A is hard to find and prove the answer comparing with another D2A.

B also harder than before, but not as much as A and C.

C is awesome. It's very easy to get the wrong solution, and if then cannot get the answer after many challenges. Wrong solution using Sprague-Grundy get correct answer with all examples, and that's why I didn't even think about abandon wrong solution and do it again without anything.

D is also ad-hoc. I got answer with 1 and a half A4 paper with calculation.

Each problem was pretty satisfying, and I know that I shouldn't complain about the problem construction just because cannot getting a satisfactory result. But ABCD all are so ad-hoc.

I think one or two ad-hoc is enought for single Div2. I do not have any intent to complain. But at this point, I wonder why you brought too many ad-hoc problems...

Data of problem A is weak. As a result of me and my friends' verification, there is not a single piece of data that is $$$M \ne N \lt 2M$$$. And this is the evidence.

For example, this code which I submitted during the contest must be wrong. It gives completely wrong answer with this input.

# Input
3 2
1 1
2 2

# My Output (Wrong)
6
1 1
1 2
2 1
2 2
3 3
3 3

I sent a clarification an hour ago, and I'll update as soon as possible when I see any response. I hope that I can write up a code that will allow me to get Accepted after the data is strengthened.

And I LOVE problem B. Very beautiful problem!

Well... Downvotes tell you what is the difference.

253766687 << Yes, here are my code with dumb approach, and it passed during competition, and hacked immediately I showed this code to other ones.

I was a little disappointed with the pretest in task G. It was clearly my fault for underestimating the problem. But I was disappointed that out of 38 pretests, not a single one made simple DFS got Time Limit Exceeded in a task where you intended dp using bitfield as the correct answer.

Yes. A xor B = (A or B) - (A and B), and the candidates obtained after completing the step 2 satisfy the condition that the bit in a particular digit has a value of 1. It is because maximal value of pi or pj is 111...111(2) form.

I love D1A = D2C. Very Beautiful problem!

Server problem and investigation? Should be unrated.