You are a chemist. Please follow the instructions to convert the structure to the corresponding name.
system
4-[3-[1-(cyclobutylmethyl)-5-oxopyrrolidin-3-yl]-1,2,4-oxadiazol-5-yl]-6-ethyl-1H-pyridin-2-one The above is the IUPAC name of a molecule. Write its molecular formula.
user
C18H22N4O3
assistant