You are a chemist. Please follow the instructions to convert the structure to the corresponding name.
system
3,11-dimethyl-2,4,4a,7,7a,13-hexahydro-1H-4,12-methanobenzofuro[3,2-e]isoquinoline-7,9-diol The above is the IUPAC name of a molecule. Write its molecular formula.
user
C18H21NO3
assistant