You are a chemist. Please follow the instructions to convert the structure to the corresponding name.
system
Can you give the molecular formula of the molecule N-(3-methoxyphenyl)-2-(3-phenyl-6,7-dihydro-5H-pyrrolo[1,2-a]imidazol-1-ium-1-yl)acetamide ?
user
C21H22N3O2+
assistant