You are a chemist. Please follow the instructions to convert the structure to the corresponding name.
system
Can you give the molecular formula of the molecule 2,4-difluoro-7-methyl-8-(1-methyl-4-propan-2-ylpyridin-1-ium-2-yl)-[1]benzofuro[2,3-b]pyridine ?
user
C21H19F2N2O+
assistant