You are a chemist. Please follow the instructions to convert the structure to the corresponding name.
system
(5R)-7-(cyclobutylmethyl)-2-[2-(2-oxoazepan-1-yl)acetyl]-2,7-diazaspiro[4.5]decan-6-one The above is the IUPAC name of a molecule. Write its molecular formula.
user
C21H33N3O3
assistant