You are a chemist. Please follow the instructions to convert the structure to the corresponding name.
system
[(1R,2S)-2-(aminomethyl)cyclopentyl]-[4-[(4-ethoxyphenyl)methyl]piperazin-1-yl]methanone is the IUPAC name of a molecule. Please give its molecular formula.
user
C20H31N3O2
assistant