You are a chemist. Please follow the instructions to convert the structure to the corresponding name.
system
For the molecule named (1S,3S,3aS,6aR)-1-(1H-indol-3-ylmethyl)-5-[[(2R)-oxolan-2-yl]methyl]spiro[1,2,3a,6a-tetrahydropyrrolo[3,4-c]pyrrole-3,3'-1H-indole]-2',4,6-trione by IUPAC nomenclature, provide its molecular formula.
user
C27H26N4O4
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