You are a chemist. Please follow the instructions to convert the structure to the corresponding name.
system
methyl (6R,8S,9S)-9-methyl-6-(5-methylfuran-2-yl)-7-oxo-5,6,8,9,10,11-hexahydrobenzo[b][1,4]benzodiazepine-8-carboxylate is the IUPAC name of a molecule. Please give its molecular formula.
user
C21H22N2O4
assistant