내가 돌아왔다! (Hello, Codeforces!)

I am thrilled to introduce you to Codeforces Round #633. Following are basic information:

• This contest will take place on Apr/12/2020 17:05 (Moscow time).
• The round is rated for all participants who can understand this announcement. There will be two divisions.
• There are 5 problems in each division and you will have 2 hours to solve it.
• Score distribution will be announced later.

Followings are contributors:

• Authors: McDic — All Div.2 problems and Div1D, tzuyu_chou — Div1E
• Coordinator: antontrygubO_o
• Testers:
  • Phase 1 (When this round was supposed to be Div.2): dorijanlendvaj, SoulTch, pajenegod, AryaPawn, Rahul, mcdx9524, 300iq, Nemo, tfg
  • Phase 2 (Before we knew that old Div1D can be easily googled): Um_nik, Ari, benson1029, khulegu, Sad_reacts_only, TselmegKh
  • Phase 3 (Before few days to the round): mohammedehab2002, Kuroni, xuanquang1999, JettyOller
• CF Admins: Thanks to MikeMirzayanov and his team for maintaining Codeforces and Polygon. I would like to say same sentence again as I said in my last round's announcement. Polygon is super great platform to prepare sports programming contest.

Following are some fun things that I tried for this round:

• antontrygubO_o is the most intense coordinator I have ever met. He has super high standard on ad hocs, and he rejected lots of my problems. Some example of rejection comments are below:
  • This problem is too standard.
  • Don't ask people about theorem and formula.
  • This problem is appeared in recent ptz camp with higher constraints.
  • I don't like it.
  • Rock Scissor Paper makes statement messy, because some people don't know about it.
  • D2A should be easier than this one.
  • I've found generalized version of this problem in POI.
  • Isn't this obvious?
  • Your proof is wrong.
  • This problem is not very interesting.
  • This is too (censored).
• After lots of rejections, I tried my best to make problems to be interesting. I hope you like at least some of my problems.
• This round was originally supposed to be rated for Div.2 only. However, after we completed Phase 1 testing, we found that my round is too hard for Div.2, so we added more problems and made this round to be Div.1.
• Even for some of problems which my coordinator approved, there were critical issues that made problems to be excluded. I will introduce some of my rejected problems which won't be used anymore in another post, after this contest ends.

I hope everyone can enjoy my third contest. Thanks in advance!