You are a chemist. Please follow the instructions to convert the structure to the corresponding name.
system
4-(4-hydroxy-3-methoxyphenyl)-2,7-dimethyl-5-oxo-4,6,7,8-tetrahydro-3H-quinoline-3,6-dicarboxylic acid The above is the IUPAC name of a molecule. Write its molecular formula.
user
C20H21NO7
assistant