input: 
  def is_prime(num: int) -> bool:
      """Determine if a given number is prime.
      >>> is_prime(17)
      True
      >>> is_prime(18)
      False
      """
      if num <= 1:
          return False
      for i in range(2, num):
          if num % i == 0:
              return False
      return True
  
  # Ask the user for a number
  num = int(input('Enter a number: '))
  
  # Output result
  if is_prime(num):
      print(f'{num} is a prime number.')
  else:
      print(f'{num} is not a prime number.')
  
output:     
      if num <= 1:
          return False
      for i in range(2, int(num**0.5) + 1):
          if num % i == 0:
              return False
      return True
  