You are a chemist. Please follow the instructions to convert the structure to the corresponding name.
system
What is the molecular formula of the compound with this IUPAC name 1-(3-methyl-6,8-dihydro-5H-[1,2,4]triazolo[4,3-a]pyrazin-7-yl)-2-(4-pyrrol-1-ylphenyl)ethanone ?
user
C18H19N5O
assistant