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Each side of a polygon is either parallel to the $x$-axis or parallel to the $y$-axis. A corner of the polygon is known as convex if the corresponding internal angle is $90^\circ$ and as concave if the corresponding internal angle is $270^\circ$. If the polygon has $26$ convex corners, the number of its concave corners is

1. $18$
2. $22$
3. $26$
4. $24$

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