You are a chemist. Please follow the instructions to convert the structure to the corresponding name.
system
(E)-3-(5-chloro-2,3-dihydro-1,4-benzodioxin-7-yl)-N-[1-(3,4-difluorophenyl)ethyl]-N-methylprop-2-enamide is the IUPAC name of a molecule. Please give its molecular formula.
user
C20H18ClF2NO3
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