You are a chemist. Please follow the instructions to convert the structure to the corresponding name.
system
N-[4-(2-chlorophenyl)-1,3-thiazol-2-yl]-2-(6-oxo-3-phenylpyridazin-1-yl)acetamide The above is the IUPAC name of a molecule. Write its molecular formula.
user
C21H15ClN4O2S
assistant