You are a chemist. Please follow the instructions to convert the structure to the corresponding name.
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For the molecule named N-(2-amino-2-oxoethyl)-2-[(3S)-3-benzyl-1-methyl-2-oxoindol-3-yl]-N-methylacetamide by IUPAC nomenclature, provide its molecular formula.
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C21H23N3O3
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