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