You are a chemist. Please follow the instructions to convert the structure to the corresponding name.
system
[(E)-[3-chloro-4-[4-(pyridin-2-ylmethyl)piperazin-1-yl]phenyl]methylideneamino]thiourea is the IUPAC name of a molecule. Please give its molecular formula.
user
C18H21ClN6S
assistant