You are a chemist. Please follow the instructions to convert the structure to the corresponding name.
system
methyl (E)-4-[[(2S,3aS,7aS)-1-(2-thiophen-3-ylacetyl)-2,3,3a,4,5,6,7,7a-octahydroindole-2-carbonyl]amino]but-2-enoate The above is the IUPAC name of a molecule. Write its molecular formula.
user
C20H26N2O4S
assistant