You are a chemist. Please follow the instructions to convert the structure to the corresponding name.
system
methyl 2-[[(5aR,9bS)-3a-hydroxy-5a,9-dimethyl-2-oxo-4,5,6,7,8,9b-hexahydro-3H-benzo[g][1]benzofuran-3-yl]methylamino]acetate is the IUPAC name of a molecule. Please give its molecular formula.
user
C18H27NO5
assistant