You are a chemist. Please follow the instructions to convert the structure to the corresponding name.
system
(2,4-dichlorophenyl)-[3-(3,4-dihydro-1H-isoquinolin-2-yl)pyrrolidin-1-yl]methanone is the IUPAC name of a molecule. Please give its molecular formula.
user
C20H20Cl2N2O
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