You are a chemist. Please follow the instructions to convert the structure to the corresponding name.
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N-[(3-bromophenyl)methyl]-2-(8-tert-butyl-2,4-dioxo-1,3-diazaspiro[4.5]decan-3-yl)acetamide is the IUPAC name of a molecule. Please give its molecular formula.
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C21H28BrN3O3
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