You are a chemist. Please follow the instructions to convert the structure to the corresponding name.
system
For the molecule named (2S)-2-[(5S)-4-methoxy-6-methyl-7,8-dihydro-5H-[1,3]dioxolo[4,5-g]isoquinolin-5-yl]-2-phenylacetonitrile by IUPAC nomenclature, provide its molecular formula.
user
C20H20N2O3
assistant