You are a chemist. Please follow the instructions to convert the structure to the corresponding name.
system
For the molecule named 4-[4-[[(3S)-3-chlorobutan-2-yl]carbamoylamino]phenoxy]-N-methylpyridine-2-carboxamide by IUPAC nomenclature, provide its molecular formula.
user
C18H21ClN4O3
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