Given an array `arr` of positive integers sorted in a strictly increasing order, and an integer `k`.

Find the `kth` positive integer that is missing from this array.

Example 1:

    Input: arr = [2,3,4,7,11], k = 5
    Output: 9
    Explanation: The missing positive integers are [1,5,6,8,9,10,12,13,...]. The 5th missing positive integer is 9.

Example 2:

    Input: arr = [1,2,3,4], k = 2
    Output: 6
    Explanation: The missing positive integers are [5,6,7,...]. The 2nd missing positive integer is 6.

Constraints:

- `1 <= arr.length <= 1000`
- `1 <= arr[i] <= 1000`
- `1 <= k <= 1000`
- `arr[i] < arr[j]` for `1 <= i < j <= arr.length`