input: Write a function to find the most frequent element in a list using the Counter class.
  assert most_frequent([1, 1, 2, 3, 2, 4, 4]) == 1
  assert most_frequent([1, 2, 3, 4, 5, 6, 7, 8, 9, 1, 2, 2, 3, 3, 3]) == 3
  assert most_frequent(['a', 'b', 'a', 'c', 'b', 'a']) == 'a'
output: from collections import Counter
  
  def most_frequent(lst):
      counter = Counter(lst)
      most_common_element, _ = counter.most_common(1)[0]
      return most_common_element