You are a chemist. Please follow the instructions to convert the structure to the corresponding name.
system
Convert the IUPAC name of a molecule 3-methyl-1-[8-(pyridin-2-ylmethoxy)-5-oxa-2-azaspiro[3.5]nonan-2-yl]butan-1-one into molecular formula.
user
C18H26N2O3
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