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MathNet 2012 Question 36

Math Olympiad Vault · MathNet 2012

Question 36

An integer is written in each square of a $100\times100$ checkerboard. An allowed operation chooses four squares in one of the following layouts:

Question illustration

Question illustration

or any rotation of them, and adds $1$ to the number in each chosen square. The goal is to obtain, by allowed operations, a board with as few different remainders modulo $33$ as possible. What is the smallest number that can always be guaranteed?