You are a chemist. Please follow the instructions to convert the structure to the corresponding name.
system
For the molecule named (13S)-4-[(3,4-dimethoxypyridin-2-yl)methyl]-13-methyl-10-thia-3,4,6,8-tetrazatetracyclo[7.7.0.02,6.011,16]hexadeca-1(9),2,7,11(16)-tetraen-5-one by IUPAC nomenclature, provide its molecular formula.
user
C20H21N5O3S
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