code: public static int getAtomCount(IRingSet set) {
          int count = 0;
          for (IAtomContainer atomContainer : set.atomContainers()) {
              count += atomContainer.getAtomCount();
          }
          return count;
      }
docs: Return the total number of atoms over all the rings in the colllection.
  
  @param set The collection of rings
  @return  The total number of atoms