You are a chemist. Please follow the instructions to convert the structure to the corresponding name.
system
(2R,3S,5R)-5-(6-aminopurin-9-yl)-2-(hydroxymethyl)-5-(3-imidazol-1-ylpropyl)oxolan-3-ol is the IUPAC name of a molecule. Please give its molecular formula.
user
C16H21N7O3
assistant