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-[1-[2-[5-(3,5-dichlorophenyl)-1,3,4-oxadiazol-2-yl]acetyl]piperidin-4-yl]-3H-imidazo[4,5-b]pyridin-2-one by IUPAC nomenclature, provide its molecular formula.
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C21H18Cl2N6O3
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