You are a chemist. Please follow the instructions to convert the structure to the corresponding name.
system
ethyl (2-pyridin-4-yl-3-thiophen-2-yl-6,7-dihydro-5H-pyrrolizin-1-yl) carbonate is the IUPAC name of a molecule. Please give its molecular formula.
user
C19H18N2O3S
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