You are a chemist. Please follow the instructions to convert the structure to the corresponding name.
system
N-(3-chlorophenyl)-4-(6,7-dihydro-5H-cyclopenta[c]pyridazin-3-yl)piperazine-1-carboxamide is the IUPAC name of a molecule. Please give its molecular formula.
user
C18H20ClN5O
assistant