You are a chemist. Please follow the instructions to convert the structure to the corresponding name.
system
Translate the chemical IUPAC name 2-[(2-methyl-6-propan-2-ylpyridin-3-yl)methyl]spiro[3,4-dihydropyrrolo[1,2-a]pyrazine-1,3'-piperidine] into its molecular formula.
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C21H30N4
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