You are a chemist. Please follow the instructions to convert the structure to the corresponding name.
system
N-(2,4-difluorophenyl)-2-[4-(2-hydroxyphenyl)piperazin-1-ium-1-yl]acetamide The above is the IUPAC name of a molecule. Write its molecular formula.
user
C18H20F2N3O2+
assistant