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MathNet 2017-part-06 — 176 problems (EN–VI) Question 127

Math Olympiad Vault · MathNet 2017-part-06 — 176 problems (EN–VI)

Question 127

Let $n \ge 2$ be a positive integer. There is an $n \times n$ chessboard-shaped region, each unit cell of which is a park. Each park contains some cats (the number of cats is a non-negative integer). To manage the cats, the administration performs operations on the parks. In each operation the administration chooses one park:
(1) the chosen park must contain at least as many cats as the number of parks adjacent to it;
(2) after park $A$ is chosen, for each park $B$ adjacent to it, the administration drives one cat from $A$ to $B$ (two parks are called adjacent if and only if they share a common edge).
Let $m$ be the total number of cats in all parks. Find the smallest $m$ for which there is an initial distribution of cats such that, by choosing the park for each operation appropriately, the administration can perform infinitely many operations.