You are a chemist. Please follow the instructions to convert the structure to the corresponding name.
system
For the molecule named 3-methyl-N-[[4-(2-methylpropyl)morpholin-2-yl]methyl]-1-oxo-4H-isochromene-3-carboxamide by IUPAC nomenclature, provide its molecular formula.
user
C20H28N2O4
assistant