You are a chemist. Please follow the instructions to convert the structure to the corresponding name.
system
[4-[[(2S,3R)-2-(ethylcarbamoyl)-4-oxoazetidin-3-yl]methyl]pyridin-2-yl] N-[(4-methoxyphenyl)methyl]carbamate is the IUPAC name of a molecule. Please give its molecular formula.
user
C21H24N4O5
assistant