You are a chemist. Please follow the instructions to convert the structure to the corresponding name.
system
N-(3,5-dimethylphenyl)-3-(1,9-dimethyl-1,4,9-triazaspiro[5.5]undecan-4-yl)-3-oxopropanamide is the IUPAC name of a molecule. Please give its molecular formula.
user
C21H32N4O2
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