You are a chemist. Please follow the instructions to convert the structure to the corresponding name.
system
(2R)-2-(5,6-dimethylthieno[2,3-d]pyrimidin-4-yl)sulfanyl-1-[(2S)-2-methyl-2,3-dihydroindol-1-yl]propan-1-one is the IUPAC name of a molecule. Please give its molecular formula.
user
C20H21N3OS2
assistant