You are a chemist. Please follow the instructions to convert the structure to the corresponding name.
system
2-(5,6-dimethylthieno[2,3-d]pyrimidin-4-yl)sulfanyl-N-ethyl-N-[(4-oxo-3H-quinazolin-2-yl)methyl]acetamide The above is the IUPAC name of a molecule. Write its molecular formula.
user
C21H21N5O2S2
assistant