You are a chemist. Please follow the instructions to convert the structure to the corresponding name.
system
4,7-dibromo-2,2-dimethyl-3-oxido-4,5,6,7-tetrahydrobenzimidazol-1-ium 1-oxide is the IUPAC name of a molecule. Please give its molecular formula.
user
C9H12Br2N2O2
assistant