input: Write a function to find the three most common elements in a list.
  assert most_common([1, 4, 2, 6, 7, 5, 1, 10, 4]) == [1, 4, 2]
  assert most_common([1, 1, 1, 2, 2, 3]) == [1, 2, 3]
  assert most_common([10, 20, 30, 40, 50, 20, 30, 30]) == [30, 20, 10]
output: from collections import Counter
  
  def most_common(lst):
      counter = Counter(lst)
      most_common_elements = counter.most_common(3)
      return [element for element, count in most_common_elements]