def CalculateArithmeticTopoIndex(mol):
    """
    Arithmetic topological index by Narumi
        Parameters:
            mol: RDKit molecule object
        Returns:
            Arto: Arithmatic topological index
    """
    nAtoms = mol.GetNumAtoms()
    nBonds = mol.GetNumBonds()
    res = 2. * nBonds / nAtoms
    return res