You are a chemist. Please follow the instructions to convert the structure to the corresponding name.
system
Can you give the molecular formula of the molecule 3-ethyl-7-[(1-oxo-3,4-dihydro-2H-isoquinolin-7-yl)sulfonyl]-6,8-dihydro-5H-pyrido[3,4-d]pyrimidin-4-one ?
user
C18H20N4O4S
assistant