You are a chemist. Please follow the instructions to convert the structure to the corresponding name.
system
6-(1H-indol-2-ylmethyl)-2-oxo-1,5,7,8-tetrahydro-1,6-naphthyridine-3-carboxylic acid is the IUPAC name of a molecule. Please give its molecular formula.
user
C18H17N3O3
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