You are a chemist. Please follow the instructions to convert the structure to the corresponding name.
system
(3S)-2'-amino-5-methoxy-2,5'-dioxospiro[1H-indole-3,4'-7,8-dihydro-6H-chromene]-3'-carbonitrile is the IUPAC name of a molecule. Please give its molecular formula.
user
C18H15N3O4
assistant