You are a chemist. Please follow the instructions to convert the structure to the corresponding name.
system
(6R)-10-ethyl-1-methyl-4-[[3-(2-methylpropyl)imidazol-4-yl]methyl]-1,4,10-triazaspiro[5.6]dodecan-9-one is the IUPAC name of a molecule. Please give its molecular formula.
user
C20H35N5O
assistant