You are a chemist. Please follow the instructions to convert the structure to the corresponding name.
system
[1-[(3,4-difluorophenyl)methyl]-3-methyl-4,5,6,7-tetrahydroindol-2-yl]-pyrrolidin-1-ylmethanone is the IUPAC name of a molecule. Please give its molecular formula.
user
C21H24F2N2O
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