input: Write a python function to add an element to a list and compute its median.
  assert median_finder([1, 3, 4], 2) == 2.5
  assert median_finder([1, 2, 3, 4], 5) == 3
  assert median_finder([10, 20, 30, 40], 35) == 30.0
output: def median_finder(lst, element):
      lst.append(element)
      lst.sort()
      n = len(lst)
      if n % 2 == 1:
          return lst[n // 2]
      else:
          return (lst[n // 2 - 1] + lst[n // 2]) / 2