<SYSTEM_TASK:>
Solve the following problem using Python, implementing the functions described below, one line at a time
<END_TASK>
<USER_TASK:>
Description:
 def jaccardIndex(s1, s2, stranded=False):
 """ Compute the Jaccard index for two collections of genomic intervals :param s1: the first set of genomic intervals :param s2: the second set of genomic intervals :param stranded: if True, treat regions on different strands as not intersecting each other, even if they occupy the same genomic region. :return: Jaccard index """


  def count(s):
    """ sum the size of regions in s. """
    tot = 0
    for r in s:
      tot += len(r)
    return tot

  if stranded:
    raise GenomicIntervalError("Sorry, stranded mode for computing Jaccard " +
                               "index hasn't been implemented yet.")

  s1 = collapseRegions(s1)
  s2 = collapseRegions(s2)
  intersection = regionsIntersection(s1, s2)
  c_i = count(intersection)
  return c_i / float(count(s1) + count(s2) - c_i)