You are a chemist. Please follow the instructions to convert the structure to the corresponding name.
system
For the molecule named [4-(1,3-benzothiazol-2-ylmethyl)piperazin-1-yl]-(2-hydroxy-5-methoxyphenyl)methanone by IUPAC nomenclature, provide its molecular formula.
user
C20H21N3O3S
assistant