You are a chemist. Please follow the instructions to convert the structure to the corresponding name.
system
For the molecule named (E)-1-(5,8-dichloro-6,7-dimethoxy-3,4-dihydro-1H-isoquinolin-2-yl)-3-(6-methoxypyridin-3-yl)prop-2-en-1-one by IUPAC nomenclature, provide its molecular formula.
user
C20H20Cl2N2O4
assistant