You are a chemist. Please follow the instructions to convert the structure to the corresponding name.
system
3-(2-chloro-1,3-thiazol-5-yl)-7-hydroxy-1,8-dimethyl-6-(3-methylphenyl)-2,3-dihydroimidazo[1,2-a]pyrimidin-8-ium-5-one is the IUPAC name of a molecule. Please give its molecular formula.
user
C18H18ClN4O2S+
assistant