You are a chemist. Please follow the instructions to convert the structure to the corresponding name.
system
(Z)-2-(4-chlorophenyl)-3-[1-(4-hydroxyphenyl)-2,5-dimethylpyrrol-3-yl]prop-2-enenitrile is the IUPAC name of a molecule. Please give its molecular formula.
user
C21H17ClN2O
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