You are a chemist. Please follow the instructions to convert the structure to the corresponding name.
system
3-[4-(5-bromopyridin-2-yl)piperazin-1-yl]-N-(2,5-dichlorophenyl)propanamide is the IUPAC name of a molecule. Please give its molecular formula.
user
C18H19BrCl2N4O
assistant