You are a chemist. Please follow the instructions to convert the structure to the corresponding name.
system
N-[3-[(2R)-1-(6-chloropyrazin-2-yl)propan-2-yl]phenyl]-2-methylpyridine-4-carboxamide is the IUPAC name of a molecule. Please give its molecular formula.
user
C20H19ClN4O
assistant