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 5-bromo-1-[(2-chlorophenyl)methyl]-3-[2-(furan-2-yl)-2-oxoethyl]-3-hydroxyindol-2-one is given. What is its corresponding molecular formula?
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C21H15BrClNO4
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