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