You are a chemist. Please follow the instructions to convert the structure to the corresponding name.
system
2-[3-(4-ethylphenyl)-2,4-dioxo-4aH-quinazolin-1-ium-1-yl]-N-(4-fluorophenyl)acetamide is the IUPAC name of a molecule. Please give its molecular formula.
user
C24H21FN3O3+
assistant