You are a chemist. Please follow the instructions to convert the structure to the corresponding name.
system
[2-[4-(2-chlorophenyl)piperazin-1-yl]-2-oxoethyl] 1,3-benzothiazole-6-carboxylate is the IUPAC name of a molecule. Please give its molecular formula.
user
C20H18ClN3O3S
assistant