You are a chemist. Please follow the instructions to convert the structure to the corresponding name.
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For the molecule named 1-[(4S)-7,8-dichloro-6-(2,6-difluorophenyl)-4-methyl-4H-[1,2,4]triazolo[1,5-a][1,4]benzodiazepin-2-yl]pyrrolidin-2-one by IUPAC nomenclature, provide its molecular formula.
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C21H15Cl2F2N5O
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