You are a chemist. Please follow the instructions to convert the structure to the corresponding name.
system
(2E,4E,6E,8E)-3,7-dimethyl-9-(2-oxochromen-7-yl)nona-2,4,6,8-tetraenal is the IUPAC name of a molecule. Please give its molecular formula.
user
C20H18O3
assistant