You are a chemist. Please follow the instructions to convert the structure to the corresponding name.
system
Translate the chemical IUPAC name (3R,4S)-4-[(1R)-1-hydroxy-2-methylidene-3-oxobutyl]-1-pent-4-ynyl-3-phenoxyazetidin-2-one into its molecular formula.
user
C19H21NO4
assistant