You are a chemist. Please follow the instructions to convert the structure to the corresponding name.
system
[(2R,3S,4R,5R)-2-(2-amino-6-oxo-8-phenylmethoxy-1H-purin-9-yl)-5-ethyl-4-fluorooxolan-3-yl] acetate The above is the IUPAC name of a molecule. Write its molecular formula.
user
C20H22FN5O5
assistant