Codeforces Global Round 17

Hello, Codeforces!

It is the fifth round of a 2021 series of Codeforces Global Rounds. The rounds are open and rated for everybody.

The prizes for this round:

30 best participants get a t-shirt.
20 t-shirts are randomly distributed among those with ranks between 31 and 500, inclusive.

The prizes for the 6-round series in 2021:

In each round top-100 participants get points according to the table.
The final result for each participant is equal to the sum of points he gets in the four rounds he placed the highest.
The best 20 participants over all series get sweatshirts and place certificates.

Thanks to XTX, which in 2021 supported the global rounds initiative!

The problems were written and prepared by AliShahali1382(Ali Shahali), AmShZ(AmirMohammad ShahRezaei), DeadlyCritic(MohammadHossein Paydar), Keshi(Alireza Keshavarz), alireza_kaviani(Alireza Kaviani).

We would like to thank these people:

antontrygubO_o, for coordinating and helping a lot to make this round happen.
Tet(Soroush Sahraei) and -zeus-(Alireza Samimi) for giving ideas for some problems.
our testers for testing and providing helpful feedbacks: gamegame, Kalam, Amoo_Safar, prabowo, dorijanlendvaj, nor, ArshiaDadras, -zeus-, ijxjdjd, Sohsoh84, chctxdy68, m371, naman1601, mblazev, fatemetmhr, hiva_, manish.17, Saman., SMahdi, Vjovein.
again gamegame for being an orz tester and ACing all of our problems!
MikeMirzayanov for codeforces and polygon platform!

You will have 3 hours to solve 9 problems. As usual, it is highly recommended to read all problems!

The rating distribution will be announced at least 5 minutes before the round starts! :)

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