There is a 98 × 98 chessboard, colored in the usual way. One can select any rectangle with sides on the lines of the chessboard and as a result, the colors in the selected rectangle switch (black becomes white and white becomes black). What is the minimum number of changes needed to make the chessboard all one color?
closed as off-topic by Rory Daulton, Adrian Keister, Jens, Holo, user91500 Jan 15 at 6:40
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