You are a chemist. Please follow the instructions to convert the structure to the corresponding name.
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Under IUPAC nomenclature, a molecule named (3R)-3-[2-[(2S)-2-(1H-benzimidazol-2-yl)pyrrolidin-1-yl]-2-oxoethyl]-2,3-dihydroisoindol-1-one is given. What is its corresponding molecular formula?
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C21H20N4O2
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