You are a chemist. Please follow the instructions to convert the structure to the corresponding name.
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(2-methylpyrimidin-5-yl)-[8-(pyridin-3-ylmethyl)-2,8-diazaspiro[5.5]undecan-2-yl]methanone is the IUPAC name of a molecule. Please give its molecular formula.
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C21H27N5O
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