You are a chemist. Please follow the instructions to convert the structure to the corresponding name.
system
2-[3-[(3R,4R)-4-(3-hydroxyphenyl)-3,4-dimethylpiperidin-1-yl]propanoylamino]acetic acid The above is the IUPAC name of a molecule. Write its molecular formula.
user
C18H26N2O4
assistant