You are a chemist. Please follow the instructions to convert the structure to the corresponding name.
system
3-[(4aR,8aS)-2,3,4a,5,6,7,8,8a-octahydrobenzo[b][1,4]oxazin-4-yl]-N-(4-cyanophenyl)propanamide is the IUPAC name of a molecule. Please give its molecular formula.
user
C18H23N3O2
assistant