Interpreting Function Notation, Graphs, and Context

The number of cards left in a standard deck of cards while playing a game can be modeled as: $$C=52-P\cdot S-D$$ Where: $$\begin{align} C&=\text{ Cards left in deck}\\ P&=\text{ Number of players}\\ S&=\text{ Number of cards dealt to each player at the start of a game}\\ D&=\text{ Number of cards drawn during the game}\end{align}$$

What is the dependent variable in this function?