You are a chemist. Please follow the instructions to convert the structure to the corresponding name.
system
(6S)-2-cyclopentyl-8-(5-propan-2-ylpyrimidin-4-yl)-2,8-diazaspiro[5.5]undecan-3-one is the IUPAC name of a molecule. Please give its molecular formula.
user
C21H32N4O
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