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-[(4-chlorophenyl)methyl]-2-[4-[(3-methylphenyl)methyl]-2,3-dioxopiperazin-1-yl]acetamide by IUPAC nomenclature, provide its molecular formula.
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C21H22ClN3O3
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