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