You are given an array `points` containing the coordinates of points on a 2D plane, sorted by the x-values, where `points[i] = [xi, yi]` such that `xi < xj` for all `1 <= i < j <= points.length`. You are also given an integer `k`.

Return the maximum value of the equation `yi + yj + |xi - xj|` where `|xi - xj| <= k` and `1 <= i < j <= points.length`.

It is guaranteed that there exists at least one pair of points that satisfy the constraint `|xi - xj| <= k`.

Example 1:

    Input: points = [[1,3],[2,0],[5,10],[6,-10]], k = 1
    Output: 4
    Explanation: The first two points satisfy the condition |xi - xj| <= 1 and if we calculate the equation we get 3 + 0 + |1 - 2| = 4. Third and fourth points also satisfy the condition and give a value of 10 + -10 + |5 - 6| = 1.
    No other pairs satisfy the condition, so we return the max of 4 and 1.

Example 2:

    Input: points = [[0,0],[3,0],[9,2]], k = 3
    Output: 3
    Explanation: Only the first two points have an absolute difference of 3 or less in the x-values, and give the value of 0 + 0 + |0 - 3| = 3.

Constraints:

- `2 <= points.length <= 105`
- `points[i].length == 2`
- `-108 <= xi, yi <= 108`
- `0 <= k <= 2 * 108`
- `xi < xj` for all `1 <= i < j <= points.length`
- `xi` form a strictly increasing sequence.