You are a chemist. Please follow the instructions to convert the structure to the corresponding name.
system
N-(4-acetylphenyl)-2-(1,10b-dihydropyrazolo[1,5-c]quinazolin-5-ylsulfanyl)propanamide is the IUPAC name of a molecule. Please give its molecular formula.
user
C21H20N4O2S
assistant