input: Write a python function to find the maximum number in a list.
  assert find_max([1, 2, 3, 4, 5, 6, 7, 8, 9]) == 9
  assert find_max([10, 20, 45, 67, 84, 93]) == 93
  assert find_max([5, 7, 9, 8, 6, 4, 3]) == 9
output: def find_max(lst):
      return max(lst)