You are a chemist. Please follow the instructions to convert the structure to the corresponding name.
system
1-[4-amino-5-(2-fluoropyridine-4-carboximidoyl)pyridin-2-yl]-3-[(1R)-1-(3-chloro-4-fluorophenyl)ethyl]urea is the IUPAC name of a molecule. Please give its molecular formula.
user
C20H17ClF2N6O
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