You are a chemist. Please follow the instructions to convert the structure to the corresponding name.
system
(2R)-2-[4-(methylamino)quinazolin-2-yl]sulfanyl-1-[(2R)-2-methyl-2,3-dihydroindol-1-yl]propan-1-one The above is the IUPAC name of a molecule. Write its molecular formula.
user
C21H22N4OS
assistant