You are a chemist. Please follow the instructions to convert the structure to the corresponding name.
system
(5E)-3-[(2R)-butan-2-yl]-5-[[1-(3-chloro-2-methylphenyl)-2,5-dimethylpyrrol-3-yl]methylidene]-1,3-thiazolidine-2,4-dione is the IUPAC name of a molecule. Please give its molecular formula.
user
C21H23ClN2O2S
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