You are a chemist. Please follow the instructions to convert the structure to the corresponding name.
system
(3aS,9bS)-3a-methyl-8-phenylmethoxy-2,3,4,9b-tetrahydro-1H-chromeno[3,4-b]pyrrole The above is the IUPAC name of a molecule. Write its molecular formula.
user
C19H21NO2
assistant