You are a chemist. Please follow the instructions to convert the structure to the corresponding name.
system
For the molecule named 2-[5-fluoro-1-methyl-6-(2-methylphenyl)pyridin-1-ium-3-yl]-1,3-benzothiazole by IUPAC nomenclature, provide its molecular formula.
user
C20H16FN2S+
assistant