def undifference(first, series):
    """
    Undifferences a series
    :param first: the first actual value in the series
    :param series: the series of differences
    :return: undifferenced series
    """
    undifferenced = [first]
    for num in series:
        lastItem = undifferenced[-1]
        undifferenced.append(lastItem + num)
    return undifferenced[1:]