You are a chemist. Please follow the instructions to convert the structure to the corresponding name.
system
6-chloro-1,3-dimethyl-7-[(E)-2-morpholin-4-yl-2-phenylethenyl]pteridine-2,4-dione is the IUPAC name of a molecule. Please give its molecular formula.
user
C20H20ClN5O3
assistant