You are a chemist. Please follow the instructions to convert the structure to the corresponding name.
system
For the molecule named (3S)-N-cyclopentyl-2-(3-methoxyphenyl)-3-methyl-1-oxo-4H-pyrazino[1,2-a]indole-3-carboxamide by IUPAC nomenclature, provide its molecular formula.
user
C25H27N3O3
assistant