input: Write a python function to find the maximum number in a list.
  assert find_max([10, 3, 16, 17, 8])==17
  assert find_max([1, 2, 3, 4, 5])==5
  assert find_max([-10, -5, -3, -1])== -1
output: def find_max(lst):
      return max(lst)