You are a chemist. Please follow the instructions to convert the structure to the corresponding name.
system
(2R)-2-methoxy-N-[(S)-(2-methoxyphenyl)-(1-methylimidazol-2-yl)methyl]-2-phenylacetamide is the IUPAC name of a molecule. Please give its molecular formula.
user
C21H23N3O3
assistant