You are a chemist. Please follow the instructions to convert the structure to the corresponding name.
system
2-[7-(4-ethoxyphenyl)-1,3-dimethyl-2,4-dioxopyrimido[4,5-d]pyrimidin-5-yl]sulfanyl-N-(5-methyl-1,3,4-thiadiazol-2-yl)acetamide is the IUPAC name of a molecule. Please give its molecular formula.
user
C21H21N7O4S2
assistant