You are a chemist. Please follow the instructions to convert the structure to the corresponding name.
system
(4S,5R)-1-butyl-5-(1-cyclopentylpyrrol-2-yl)-4-pyridin-2-ylimidazolidine-2-thione The above is the IUPAC name of a molecule. Write its molecular formula.
user
C21H28N4S
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