You are a chemist. Please follow the instructions to convert the structure to the corresponding name.
system
2-[7-[(2,4-difluorophenyl)methylcarbamoyl]-8,9-dihydroxy-1-oxospiro[3,8-dihydropyrido[1,2-a]pyrazine-4,3'-oxolane]-2-yl]ethylphosphonic acid The above is the IUPAC name of a molecule. Write its molecular formula.
user
C21H24F2N3O8P
assistant