You are a chemist. Please follow the instructions to convert the structure to the corresponding name.
system
ethyl 2-[4-(difluoromethyl)-6-(1-ethyl-5-methylpyrazol-4-yl)-3-methylpyrazolo[3,4-b]pyridin-1-yl]acetate The above is the IUPAC name of a molecule. Write its molecular formula.
user
C18H21F2N5O2
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