Let
![b](/media/m/e/e/c/eec0d7323095a1f2101fc1a74d069df6.png)
be an even positive integer. We say that two different cells of a
![n \times n](/media/m/9/d/8/9d8eac5b3234425afb9f970edbfe93ef.png)
board are neighboring if they have a common side. Find the minimal number of cells on he
![n \times n](/media/m/9/d/8/9d8eac5b3234425afb9f970edbfe93ef.png)
board that must be marked so that any cell marked or not marked) has a marked neighboring cell.
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Let $b$ be an even positive integer. We say that two different cells of a $n \times n$ board are neighboring if they have a common side. Find the minimal number of cells on he $n \times n$ board that must be marked so that any cell marked or not marked) has a marked neighboring cell.