Problem: Submarine Navigator

As part of an underwater research mission, you're piloting a submarine to map the ocean floor. The submarine responds to a series of commands to move through the water. Your goal is to calculate the final horizontal position and depth after following the planned course.

Commands:
forward X: Increases your horizontal position by X units.
down X: Increases your depth by X units.
up X: Decreases your depth by X units (opposite of down).

You start at a horizontal position of 0 and a depth of 0. The goal is to compute the product of the final horizontal position and depth.