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([0, 0, 0, 1, 2, 3, 0]) == 0
output: def most_frequent(lst):
      return max(set(lst), key=lst.count)