You are a chemist. Please follow the instructions to convert the structure to the corresponding name.
system
[(4aS,7aR)-4-benzyl-2,3,4a,5,7,7a-hexahydropyrrolo[3,4-b][1,4]oxazin-6-yl]-(furan-2-yl)methanone The above is the IUPAC name of a molecule. Write its molecular formula.
user
C18H20N2O3
assistant