How to solve this problem of CEOI Mirror 2020?

Правка en1, от Rock2000, 2020-10-16 16:51:21

Can someone please tell me how to solve this problem? I saw the editorial but couldn't understand how to solve the subtask 7. Thanks in advance.

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en1 Английский Rock2000 2020-10-16 16:51:21 239 Initial revision (published)