You are a chemist. Please follow the instructions to convert the structure to the corresponding name.
system
(2R)-1-[4-[2-(4-amino-2-chloro-6-methylpyrimidin-5-yl)ethyl]piperidin-1-yl]-2-methyl-4-pyridazin-3-ylbutane-1,4-dione is the IUPAC name of a molecule. Please give its molecular formula.
user
C21H27ClN6O2
assistant