def read_rxn_counts_line_v2000(lr):
    """Reads the next line from the lr line reader which is expected to
contain the numbers of reactants and products in the 'rrrppp' format and
returns the numbers."""
    line = lr.get_line()
    num_reactants = int(line[:3])
    num_products = int(line[3:6])
    return num_reactants, num_products