You are a chemist. Please follow the instructions to convert the structure to the corresponding name.
system
For the molecule named (2E)-2-[(6-chloro-7-methyl-4,5-dihydrobenzo[e][1,3]benzothiazol-2-yl)hydrazinylidene]-3-(2-nitrophenyl)propanoic acid by IUPAC nomenclature, provide its molecular formula.
user
C21H17ClN4O4S
assistant