You are a chemist. Please follow the instructions to convert the structure to the corresponding name.
system
(Z)-3-(3,4-dichlorophenyl)-N-[4-(difluoromethoxy)phenyl]-3-hydroxy-2-pyridin-1-ium-1-ylprop-2-enethioamide is the IUPAC name of a molecule. Please give its molecular formula.
user
C21H15Cl2F2N2O2S+
assistant