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
- $18$
- $22$
- $26$
- $24$