input: Write a python function to find the most frequent element in a list.
  assert most_frequent([1, 2, 3, 3, 2, 1, 3, 3, 2, 2, 2, 2]) == 2
  assert most_frequent([4, 5, 6, 7, 8, 8, 8, 8, 7, 6, 5, 4]) == 8
  assert most_frequent([1, 1, 1, 2, 2, 2, 3, 3, 3]) == 1
output: def most_frequent(lst):
      from collections import Counter
      count = Counter(lst)
      return count.most_common(1)[0][0]