You are a chemist. Please follow the instructions to convert the structure to the corresponding name.
system
For the molecule named 1-(3-chlorophenyl)-3-(2-hydroxyethylsulfanyl)-4-(4-propan-2-yloxyphenyl)pyrrole-2,5-dione by IUPAC nomenclature, provide its molecular formula.
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C21H20ClNO4S
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