You are a chemist. Please follow the instructions to convert the structure to the corresponding name.
system
methyl 2-[2-(5H-[1,2,4]triazino[5,6-b]indol-3-ylsulfanyl)butanoylamino]benzoate The above is the IUPAC name of a molecule. Write its molecular formula.
user
C21H19N5O3S
assistant