Hello Codeforces!

On Feb/28/2021 16:35 (Moscow time) we will host Codeforces Global Round 13.

It is the first 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 3.141592653, Widowmaker, Ynoi, errorgorn, oolimry, star_xingchen_c, syksykCCC.

We would also like to thank:

- Great antontrygubO_o for
~~rejecting problems~~greatest coordination! - tfg, dvdg6566, cjy2003, Tlatoani, purinliang, user14767553, bensonlzl, wlzhouzhuan, maomao90, huangqr, mollnn, golions, b23v, qlf9, gamegame, Myrcella, kefaa2, Dormi, flaviu2001, Karavaiev, wh0816, kdjonty31, socho, Karry5307, dXqwq, KagamineRin, hzkmd, syh0313, Nanako, sunsiyu, zkdxl, Pecco, ODT for testing the round and
~~sticking on difficult problems~~providing valuable feedback to the problems. - froggyzhang, paulzrm, mejiamejia for giving great
~~rejected~~problems and many interesting ideas. - MikeMirzayanov for great Codeforces and Polygon platforms!
- And You, for participating! Your participation in this round will allow
~~our emperor~~Anton to reject more problems.

You will have 3 hours to solve 9 problems. We encourage you to read all the problems ~~and solve them all~~.

One of these problems is interactive, please see the guide of interactive problems if you are not familiar with it.

**UPD1:** Scoring distribution: 500-750-1000-1250-1750-2000-2250-3000-5000

**UPD2:** Tutorial published.

**UPD3:** System testing finished, congrats to the winners!