input: 
  def max_num(nums: List[int]) -> int:
      """ Given a list of integers, find and return the maximum number in the list.
      
      >>> max_num([9, 2, 5, 6, 4, 1])
      9
      >>> max_num([10, 22, 8, 15, 7])
      22
      """
      max_num = nums[0]
      
      for num in nums:
          if num > max_num:
              max_num = num
      
      return max_num
  
output:     max_num = nums[0]
      
      for num in nums:
          if num > max_num:
              max_num = num
      
      return max_num