You are a chemist. Please follow the instructions to convert the structure to the corresponding name.
system
For the molecule named (8aR)-2-[(S)-[1-(2-methylbutan-2-yl)tetrazol-5-yl]-thiophen-2-ylmethyl]-2,3,4,5,6,7,8,8a-octahydro-1H-pyrrolo[1,2-a]pyrazine-2,5-diium by IUPAC nomenclature, provide its molecular formula.
user
C18H30N6S+2
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