You are a chemist. Please follow the instructions to convert the structure to the corresponding name.
system
tetrapotassium;2,17-diazaheptacyclo[16.12.0.03,16.04,13.06,11.019,28.021,26]triaconta-1(30),2,4(13),6,8,10,15,17,19(28),21,23,25-dodecaene-5,12,20,27-tetrolate The above is the IUPAC name of a molecule. Write its molecular formula.
user
C28H18K4N2O4
assistant