You are a chemist. Please follow the instructions to convert the structure to the corresponding name.
system
Please write the molecular formula of the molecule (1R,4Z,5S)-8-methyl-2,4-bis(1H-pyrrol-2-ylmethylidene)-8-azoniabicyclo[3.2.1]octan-3-one .
user
C18H20N3O+
assistant