You are a chemist. Please follow the instructions to convert the structure to the corresponding name.
system
(2S,5R)-5-(4-fluorophenyl)-3-oxo-2-(6,7,8,9-tetrahydro-5H-[1,2,4]triazolo[4,3-a]azepin-3-yl)hexanenitrile is the IUPAC name of a molecule. Please give its molecular formula.
user
C19H21FN4O
assistant