You are a chemist. Please follow the instructions to convert the structure to the corresponding name.
system
What is the molecular formula of the compound with this IUPAC name N-ethyl-N-[(4-methoxyphenyl)methyl]-7-methyl-4-oxopyrido[1,2-a]pyrimidine-3-carboxamide ?
user
C20H21N3O3
assistant