You are a chemist. Please follow the instructions to convert the structure to the corresponding name.
system
Translate the chemical IUPAC name (4R,7aR)-3-(cyclopropylmethyl)-4a,9-dihydroxy-3-oxido-2,4,5,6,7a,13-hexahydro-1H-4,12-methanobenzofuro[3,2-e]isoquinolin-3-ium-7-one into its molecular formula.
user
C20H23NO5
assistant