code: public static final int getNrAtoms(Structure s) {
  
  		int nrAtoms = 0;
  
  		Iterator<Group> iter = new GroupIterator(s);
  
  		while (iter.hasNext()) {
  			Group g = iter.next();
  			nrAtoms += g.size();
  		}
  
  		return nrAtoms;
  	}
docs: Count how many Atoms are contained within a Structure object.
  
  @param s
  the structure object
  @return the number of Atoms in this Structure