input: 
  from typing import List
  
  def max_num(list: List[int]) -> int:
      """ Function to find the maximum number in a list.
      >>> max_num([9, 2, 5, 6, 4, 1])
      9
      >>> max_num([-1, -2, -3, -4, -5])
      -1
      """
      max_num = list[0]
      
      for num in list:
          if num > max_num:
              max_num = num
      
      return max_num
  
output:     max_num = list[0]
      
      for num in list:
          if num > max_num:
              max_num = num
      
      return max_num