You are a chemist. Please follow the instructions to convert the structure to the corresponding name.
system
7-[3-methyl-2-(2-methylphenyl)benzimidazol-3-ium-1-yl]-6,8-di(propan-2-yl)-[1]benzofuro[2,3-b]pyrazine The above is the IUPAC name of a molecule. Write its molecular formula.
user
C31H31N4O+
assistant