def duration_as_string(years, months):
    """ Return duration as printable string """
    duration_y = ''
    duration_m = ''
    if years > 1:
        duration_y = '{} years'.format(years)
    elif years == 1:
        duration_y = '1 year'
    if months > 1:
        duration_m = '{} months'.format(months)
    elif months == 1:
        duration_m = '1 month'
    if duration_y and duration_m:
        return '{}, {}'.format(duration_y, duration_m)

    return duration_y + duration_m