You are a chemist. Please follow the instructions to convert the structure to the corresponding name.
system
(2S)-5-amino-2-[(2-methylpropan-2-yl)oxycarbonylamino]-6-oxo-6-phenylmethoxyhexanoic acid is the IUPAC name of a molecule. Please give its molecular formula.
user
C18H26N2O6
assistant