You are a chemist. Please follow the instructions to convert the structure to the corresponding name.
system
8-[(2-chloro-6-fluorophenyl)methyl]-3-phenyl-1,4,8-triazaspiro[4.5]dec-3-en-2-one is the IUPAC name of a molecule. Please give its molecular formula.
user
C20H19ClFN3O
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