new_contents: # Simple function for primeness test
  def is_prime(number):
  
    import math
  
    limit = int(math.sqrt(number)) + 1
  
    if number == 2:
      return True
    if number % 2 == 0:
      return False
    for i in range(3, limit, 2):
      if number % i == 0:
        return False
  
    return True
  
  import math
  
  large_number = 600851475143
  limit_large_number = int(math.sqrt(large_number))
  answer = -1
  
  for i in range(2, limit_large_number):
    if large_number % i == 0 and is_prime(i):  # short circuit evaluation FTW!
      answer = i
  
  print("Result:", answer)
  
subject: Solve problem 3 in Python