You are a chemist. Please follow the instructions to convert the structure to the corresponding name.
system
N-ethyl-4-oxo-4-(8-oxo-2,6,7,11-tetrazatricyclo[7.4.0.03,7]trideca-1(9),2,4-trien-11-yl)-N-phenylbutanamide is the IUPAC name of a molecule. Please give its molecular formula.
user
C21H23N5O3
assistant