You are a chemist. Please follow the instructions to convert the structure to the corresponding name.
system
Convert the IUPAC name of a molecule 1,3-benzothiazol-2-yl-[4-(4,6-dimethyl-1,3-benzothiazol-2-yl)piperazin-1-yl]methanone into molecular formula.
user
C21H20N4OS2
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