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