Let $c$ be a complex number.  Suppose there exist distinct complex numbers $r$, $s$, and $t$ such that for every complex number $z$, we have
\[
  (z - r)(z - s)(z - t) = (z - cr)(z - cs)(z - ct).
\]Compute the number of distinct possible values of $c$.

Let's think step by step and output the final answer within \boxed{}.
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