You are a chemist. Please follow the instructions to convert the structure to the corresponding name.
system
(2S,5aS,8aS)-1,6-dimethyl-2-[3-oxo-3-(4-piperidin-1-ium-2-ylpiperazin-1-yl)propyl]-1,2,3,4,5a,7,8,8a-octahydropyrrolo[3,2-e][1,4]diazepin-1-ium-5-one is the IUPAC name of a molecule. Please give its molecular formula.
user
C21H40N6O2+2
assistant