You are a chemist. Please follow the instructions to convert the structure to the corresponding name.
system
For the molecule named [4-[(2-bromophenoxy)methyl]phenyl]-[(3R,4R)-3,4-diaminopyrrolidin-1-yl]methanone by IUPAC nomenclature, provide its molecular formula.
user
C18H20BrN3O2
assistant