You are a chemist. Please follow the instructions to convert the structure to the corresponding name.
system
For the molecule named 2-[4-chloro-6-[4-(cyclopentanecarbonyl)-3-methylpiperazin-1-yl]pyrimidin-2-yl]sulfanyl-1-pyrrolidin-1-ylethanone by IUPAC nomenclature, provide its molecular formula.
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C21H30ClN5O2S
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