You are a chemist. Please follow the instructions to convert the structure to the corresponding name.
system
For the molecule named 2-[(4-cyanobenzoyl)-(4,6-difluoro-1,3-benzothiazol-2-yl)amino]ethyl-diethylazanium by IUPAC nomenclature, provide its molecular formula.
user
C21H21F2N4OS+
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