You are a chemist. Please follow the instructions to convert the structure to the corresponding name.
system
(8S)-3-[2-(cyclopentylmethoxy)ethyl]-8-methyl-7-[(5-methyl-1H-pyrazol-3-yl)methyl]-6,8-dihydro-5H-imidazo[1,2-a]pyrazine The above is the IUPAC name of a molecule. Write its molecular formula.
user
C20H31N5O
assistant