You are given two integers, `m` and `k`, and a stream of integers. You are tasked to implement a data structure that calculates the MKAverage for the stream.

The MKAverage can be calculated using these steps:

1. If the number of the elements in the stream is less than `m` you should consider the MKAverage to be `-1`. Otherwise, copy the last `m` elements of the stream to a separate container.
2. Remove the smallest `k` elements and the largest `k` elements from the container.
3. Calculate the average value for the rest of the elements rounded down to the nearest integer.

Implement the `MKAverage` class:

- `MKAverage(int m, int k)` Initializes the MKAverage object with an empty stream and the two integers `m` and `k`.
- `void addElement(int num)` Inserts a new element `num` into the stream.
- `int calculateMKAverage()` Calculates and returns the MKAverage for the current stream rounded down to the nearest integer.

Example 1:

    Input
    ["MKAverage", "addElement", "addElement", "calculateMKAverage", "addElement", "calculateMKAverage", "addElement", "addElement", "addElement", "calculateMKAverage"]
    [[3, 1], [3], [1], [], [10], [], [5], [5], [5], []]
    Output
    [null, null, null, -1, null, 3, null, null, null, 5]

    Explanation
    MKAverage obj = new MKAverage(3, 1);
    obj.addElement(3);        // current elements are [3]
    obj.addElement(1);        // current elements are [3,1]
    obj.calculateMKAverage(); // return -1, because m = 3 and only 2 elements exist.
    obj.addElement(10);       // current elements are [3,1,10]
    obj.calculateMKAverage(); // The last 3 elements are [3,1,10].
                              // After removing smallest and largest 1 element the container will be [3].
                              // The average of [3] equals 3/1 = 3, return 3
    obj.addElement(5);        // current elements are [3,1,10,5]
    obj.addElement(5);        // current elements are [3,1,10,5,5]
    obj.addElement(5);        // current elements are [3,1,10,5,5,5]
    obj.calculateMKAverage(); // The last 3 elements are [5,5,5].
                              // After removing smallest and largest 1 element the container will be [5].
                              // The average of [5] equals 5/1 = 5, return 5

Constraints:

- `3 <= m <= 105`
- `1 <= k*2 < m`
- `1 <= num <= 105`
- At most `105` calls will be made to `addElement` and `calculateMKAverage`.