You are a chemist. Please follow the instructions to convert the structure to the corresponding name.
system
(15S,16R)-16-propan-2-yloxycarbonyltetracyclo[6.6.2.02,7.09,14]hexadeca-2,4,6,9,11,13-hexaene-15-carboxylate is the IUPAC name of a molecule. Please give its molecular formula.
user
C21H19O4-
assistant