You are a chemist. Please follow the instructions to convert the structure to the corresponding name.
system
[(5S)-3-cyclopropyl-5-methyl-6,8-dihydro-5H-[1,2,4]triazolo[4,3-a]pyrazin-7-yl]-(5-methoxy-1H-indol-2-yl)methanone The above is the IUPAC name of a molecule. Write its molecular formula.
user
C19H21N5O2
assistant