You are a chemist. Please follow the instructions to convert the structure to the corresponding name.
system
(2R)-2-phenyl-N-[(1S)-1-(3-pyridin-4-yl-1H-1,2,4-triazol-5-yl)ethyl]butanamide The above is the IUPAC name of a molecule. Write its molecular formula.
user
C19H21N5O
assistant