You are a chemist. Please follow the instructions to convert the structure to the corresponding name.
system
(E)-1-[(2R)-2-(3,4-dihydro-2H-1,5-benzodioxepin-7-yl)pyrrolidin-1-yl]-3-thiophen-2-ylprop-2-en-1-one is the IUPAC name of a molecule. Please give its molecular formula.
user
C20H21NO3S
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