You are a chemist. Please follow the instructions to convert the structure to the corresponding name.
system
2-[(2-hydroxyphenyl)-(1H-imidazo[4,5-b]pyridin-2-yl)methyl]-3H-isoindol-1-one is the IUPAC name of a molecule. Please give its molecular formula.
user
C21H16N4O2
assistant