You are a chemist. Please follow the instructions to convert the structure to the corresponding name.
system
[4-(1,3-benzothiazol-2-ylmethyl)piperazin-1-yl]-(2-hydroxy-5-methylphenyl)methanone is the IUPAC name of a molecule. Please give its molecular formula.
user
C20H21N3O2S
assistant