You are a chemist. Please follow the instructions to convert the structure to the corresponding name.
system
Translate the chemical IUPAC name (4R,4aS,7aR,12bS)-4a,9-dihydroxy-3-(2-methylpropyl)-2,4,5,6,7a,13-hexahydro-1H-4,12-methanobenzofuro[3,2-e]isoquinolin-7-one into its molecular formula.
user
C20H25NO4
assistant