You are a chemist. Please follow the instructions to convert the structure to the corresponding name.
system
2-(butan-2-ylamino)-N-[1-(6,7,8,9-tetrahydro-5H-[1,2,4]triazolo[4,3-a]azepin-3-yl)ethyl]acetamide is the IUPAC name of a molecule. Please give its molecular formula.
user
C15H27N5O
assistant