Welcome to UOJ $$$\Sigma^\ast$$$ Round #1 !

We are pleased to invite you to UOJ Σ* Round #1, which will be held on Sunday, April 13, 2025 at 17:00 (UTC+8).

There will be 3 problems with subtasks, and 5 hours for you to solve them under UOJ rules (similar to IOI, but pretests are used during contest rather than system tests).

UOJ $$$\Sigma^\ast$$$ Round is a series of contest held by CommonAnts on UOJ, thanks to everyone for your contribution.

I'm sorry that the statements are provided only in Chinese language, although AI translation is useable nowadays.

In formal language, $$$\Sigma^*$$$ represents the set of "all" strings. Can you find the answer to the problem in the ocean of countless characters?

Contest Link

UOJ $$$\Sigma^\ast$$$ Round #1 is authored and prepared by CommonAnts et al, with difficulty at about $$$2100, 2800, 3500$$$ on Codeforces (I think so).

The top three participants and a special participant with condition of SHA256 48405573d9ac7a841e4860fab6036961bd8a2e7404027595e7a84b47c7771b6b will get our special gift.

PS. CommonAnts is now working on algorithms and computer science educational research, including competitive programming. Interested ones may contact us.