You are a chemist. Please follow the instructions to convert the structure to the corresponding name.
system
For the molecule named N-(2-methyl-3H-benzimidazol-5-yl)-8-(4-methylsulfinylphenyl)-[1,2,4]triazolo[1,5-a]pyrazin-2-amine by IUPAC nomenclature, provide its molecular formula.
user
C20H17N7OS
assistant