You are a chemist. Please follow the instructions to convert the structure to the corresponding name.
system
Translate the chemical IUPAC name 2-[[1-(4-propan-2-ylphenyl)imidazol-2-yl]sulfanylmethyl]pyrido[1,2-a]pyrimidin-4-one into its molecular formula.
user
C21H20N4OS
assistant