You are a chemist. Please follow the instructions to convert the structure to the corresponding name.
system
For the molecule named (2Z,5Z)-3-butyl-5-(3-methyl-1,3-benzothiazol-2-ylidene)-2-(4-oxo-3-prop-2-enyl-2-sulfanylidene-1,3-thiazolidin-5-ylidene)-1,3-thiazolidin-4-one by IUPAC nomenclature, provide its molecular formula.
user
C21H21N3O2S4
assistant