code: public static double getExactMass(HELM2Notation helm2notation) throws BuilderMoleculeException, CTKException, ChemistryException {
      /* First build one big molecule; List of molecules */
      List<AbstractMolecule> molecules = buildMolecule(helm2notation);
      return calculateExactMass(molecules);
    }
docs: method to get the ExactMass for the whole HELM
  
  @param helm2notation input HELM2Notation
  @return ExactMass of the whole HELM
  @throws BuilderMoleculeException if the whole molecule can not be built
  @throws CTKException general ChemToolKit exception passed to HELMToolKit
  @throws ChemistryException if the Chemistry Engine can not be initialized