def CalculateNumHeavyAtom(mol):
    """
    Calculation of Heavy atom counts in a molecule   
    --->nHev
    
    :param mol: molecular
    :type mol: rdkit.Chem.rdchem.Mol
    :return: the number of heavy atom counts in a molecule  
    :rtype: int
    
    """
    nHev = mol.GetNumHeavyAtoms()
    return nHev
