You are a chemist. Please follow the instructions to convert the structure to the corresponding name.
system
benzyl (5S)-5-ethyl-2-oxo-3-prop-2-ynyl-3,10-diazabicyclo[4.3.1]decane-10-carboxylate The above is the IUPAC name of a molecule. Write its molecular formula.
user
C21H26N2O3
assistant