21FA - 06 Puupuu the Puuduu

Puupuu the Pudu is a very hungry pudu. Today, she is in the mood to eat some berries. While roaming around searching for food, luck strikes her, and she finds a rectangular field full of berries! However, there are rivers that run vertically and horizontally which partition the field into $m$ rows and $n$ columns of land patches. Each of these $m\times n$ land patches contain an integer amount of