You are a chemist. Please follow the instructions to convert the structure to the corresponding name.
system
21,22-bis(1-methylpyridin-1-ium-4-yl)-23,24-bis(1-methylpyridin-4-ylidene)porphyrin-21,22,23,24-tetraium The above is the IUPAC name of a molecule. Write its molecular formula.
user
C44H40N8+6
assistant