You are a chemist. Please follow the instructions to convert the structure to the corresponding name.
system
6-bromo-4-[3-[3-(piperidin-1-ylmethyl)phenyl]-1,2,4-oxadiazol-5-yl]-1,3-dihydrobenzimidazol-2-one is the IUPAC name of a molecule. Please give its molecular formula.
user
C21H20BrN5O2
assistant