You are a chemist. Please follow the instructions to convert the structure to the corresponding name.
system
Can you give the molecular formula of the molecule (3S)-4-(furan-3-yl)spiro[1H-indole-3,7'-6,7a-dihydro-4aH-furo[2,3-f][1,3]benzodioxole]-2-one ?
user
C20H15NO5
assistant