The kth Factor of n
   Given two positive integers   n   and   k .      A factor of an integer  n  is defined as an integer  i  where  n % i == 0 .     Consider a list of all factors of  n  sorted in  ascending order , return  the  kth  factor  in this list or   return  -1  if  n  has less than  k  factors.     Example 1:   Input:  n = 12, k = 3 Output:  3 Explanation:  Factors list is [1, 2, 3, 4, 6, 12], the 3rd factor is 3.     Example 2:   Input:  n = 7, k = 2 Output:  7 Explanation:  Factors list is [1, 7], the 2nd factor is 7.     Example 3:   Input:  n = 4, k = 4 Output:  -1 Explanation:  Factors list is [1, 2, 4], there is only 3 factors. We should return -1.     Example 4:   Input:  n = 1, k = 1 Output:  1 Explanation:  Factors list is [1], the 1st factor is 1.     Example 5:   Input:  n = 1000, k = 3 Output:  4 Explanation:  Factors list is [1, 2, 4, 5, 8, 10, 20, 25, 40, 50, 100, 125, 200, 25...