You are a chemist. Please follow the instructions to convert the structure to the corresponding name.
system
(5-acetyloxy-6-bromo-3-ethoxycarbonyl-1-methylindol-2-yl)methyl-pyridin-4-ylazanium The above is the IUPAC name of a molecule. Write its molecular formula.
user
C20H21BrN3O4+
assistant