You are 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.

Constraints:

- `1 <= k <= n <= 1000`