You are a chemist. Please follow the instructions to convert the structure to the corresponding name.
system
4-(2-methyl-2,3-dihydroindole-1-carbonyl)-1-(2,3,4-trifluorophenyl)pyrrolidin-2-one is the IUPAC name of a molecule. Please give its molecular formula.
user
C20H17F3N2O2
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