You are a chemist. Please follow the instructions to convert the structure to the corresponding name.
system
1-butan-2-yl-5-[2-(4-fluorophenoxy)acetyl]-6-hydroxy-4-methyl-2-oxopyridine-3-carbonitrile is the IUPAC name of a molecule. Please give its molecular formula.
user
C19H19FN2O4
assistant