input: Write a function to find the maximum number in a list.
  assert find_max([1, 2, 300, 4, 5]) == 300
  assert find_max([-10, -20, -30, -5, -1]) == -1
  assert find_max([5, 5, 5, 5, 5]) == 5
output: def find_max(lst):
      return max(lst)