You are a chemist. Please follow the instructions to convert the structure to the corresponding name.
system
For the molecule named (3S)-3-[[(1R)-1-[4-chloro-3-(4-ethynylphenoxy)-2-fluorophenyl]propyl]amino]butanamide by IUPAC nomenclature, provide its molecular formula.
user
C21H22ClFN2O2
assistant