You are a chemist. Please follow the instructions to convert the structure to the corresponding name.
system
Convert the IUPAC name of a molecule (4S,4aR,7aS,12bR)-3-(cyclopropylmethyl)-4a-hydroxy-9-methoxy-2,4,5,6,7a,13-hexahydro-1H-4,12-methanobenzofuro[3,2-e]isoquinolin-7-one into molecular formula.
user
C21H25NO4
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