new_contents: def prime_factors(num):
      i = 2
      while i * i <= num:
          if num % i:
              i += 1
          else:
              num //= i
              yield i
      if num > 1:
          yield num
  
  if __name__ == '__main__':
      f = prime_factors(600851475143)
      print(max(f))
  
subject: complete 3 largest prime factor