You are a chemist. Please follow the instructions to convert the structure to the corresponding name.
system
(2S,3S,4R)-4-(hydroxymethyl)-3-[4-[(E)-prop-1-enyl]phenyl]-1-(pyridine-3-carbonyl)azetidine-2-carbonitrile is the IUPAC name of a molecule. Please give its molecular formula.
user
C20H19N3O2
assistant