You are a chemist. Please follow the instructions to convert the structure to the corresponding name.
system
(7S)-N-(5-chloro-1-methyl-6-oxopyridin-3-yl)-3-phenyl-5,6,7,8-tetrahydroimidazo[1,5-a]pyridine-7-carboxamide The above is the IUPAC name of a molecule. Write its molecular formula.
user
C20H19ClN4O2
assistant