input: Write a python function to find the median of a list.
  assert find_median([1, 3, 3, 6, 7, 8, 9]) == 6
  assert find_median([1, 2, 3, 4, 5, 6, 8, 9]) == 4.5
  assert find_median([3, 1, 2, 5, 3]) == 3
output: def find_median(lst):
      lst.sort()
      n = len(lst)
      mid = n // 2
      if n % 2 == 0:
          return (lst[mid - 1] + lst[mid]) / 2
      else:
          return lst[mid]