You are a chemist. Please follow the instructions to convert the structure to the corresponding name.
system
8-(4-fluorophenyl)-7-methyl-2-[(3-methylphenyl)methylsulfanyl]-3H-pyrazolo[1,5-a][1,3,5]triazin-4-one The above is the IUPAC name of a molecule. Write its molecular formula.
user
C20H17FN4OS
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