FIND MAX SHOPS

You have visited a market which is in the shape of a rectangle. At some points (x,y) there are shops with some level of royalty. You want to visit a maximum number of shops. But there are some rules to visit the shops: 1. You can visit shops with an increasing level of royalty. 2. If you visited a shop with coordinates as $X$ and $Y$ then you can visit only those shops having $x \ge X$ and $y \ge