You are a chemist. Please follow the instructions to convert the structure to the corresponding name.
system
3-[2-[(E)-(3-ethyl-5-methyl-1,3-benzothiazol-2-ylidene)methyl]-1,3-benzothiazol-3-ium-3-yl]propane-1-sulfonic acid The above is the IUPAC name of a molecule. Write its molecular formula.
user
C21H23N2O3S3+
assistant