You are a chemist. Please follow the instructions to convert the structure to the corresponding name.
system
Translate the chemical IUPAC name (4S)-N-(4-methoxyphenyl)-2-[(4-methylquinazolin-2-yl)amino]-6-oxo-4,5-dihydro-1H-pyrimidin-3-ium-4-carboxamide into its molecular formula.
user
C21H21N6O3+
assistant