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 1-[2-[(3S)-1-(5-chloropyrimidin-2-yl)-2,3-dihydroindol-3-yl]ethyl]pyrrolidin-2-one is given. What is its corresponding molecular formula?
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C18H19ClN4O
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