def find_number(formula, current_ind):
    """Returns the stoichiometry of an element from a formula

    :param formula: a string of the formula
    :param current_ind: the current parsing index
    :returns: a tuple: new parsing index, stoichiometry coefficient
    """
    k = current_ind
    while k < len(formula) and (formula[k].isdigit() or formula[k] == '.'):
        k += 1
    if k > len(formula):
        stoech = 1.0
    elif formula[current_ind:k]:
        stoech = float(formula[current_ind:k])
    else:
        stoech = 1.0
    return k, stoech
