You are a chemist. Please follow the instructions to convert the structure to the corresponding name.
system
2-ethyl-9-[(4-methyl-1,2,5-oxadiazol-3-yl)methyl]-2,9-diazaspiro[5.5]undecan-3-one is the IUPAC name of a molecule. Please give its molecular formula.
user
C15H24N4O2
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