You are a chemist. Please follow the instructions to convert the structure to the corresponding name.
system
3-methyl-7-[(5-methylpyridin-2-yl)methyl]-8-[[3-(trifluoromethoxy)phenyl]methyl]purine-2,6-dione is the IUPAC name of a molecule. Please give its molecular formula.
user
C21H18F3N5O3
assistant