Design a stack which supports the following operations.

Implement the `CustomStack` class:

- `CustomStack(int maxSize)` Initializes the object with `maxSize` which is the maximum number of elements in the stack or do nothing if the stack reached the `maxSize`.
- `void push(int x)` Adds `x` to the top of the stack if the stack hasn't reached the `maxSize`.
- `int pop()` Pops and returns the top of stack or -1 if the stack is empty.
- `void inc(int k, int val)` Increments the bottom `k` elements of the stack by `val`. If there are less than `k` elements in the stack, just increment all the elements in the stack.

Example 1:

    Input
    ["CustomStack","push","push","pop","push","push","push","increment","increment","pop","pop","pop","pop"]
    [[3],[1],[2],[],[2],[3],[4],[5,100],[2,100],[],[],[],[]]
    Output
    [null,null,null,2,null,null,null,null,null,103,202,201,-1]
    Explanation
    CustomStack customStack = new CustomStack(3); // Stack is Empty []
    customStack.push(1);                          // stack becomes [1]
    customStack.push(2);                          // stack becomes [1, 2]
    customStack.pop();                            // return 2 --> Return top of the stack 2, stack becomes [1]
    customStack.push(2);                          // stack becomes [1, 2]
    customStack.push(3);                          // stack becomes [1, 2, 3]
    customStack.push(4);                          // stack still [1, 2, 3], Don't add another elements as size is 4
    customStack.increment(5, 100);                // stack becomes [101, 102, 103]
    customStack.increment(2, 100);                // stack becomes [201, 202, 103]
    customStack.pop();                            // return 103 --> Return top of the stack 103, stack becomes [201, 202]
    customStack.pop();                            // return 202 --> Return top of the stack 102, stack becomes [201]
    customStack.pop();                            // return 201 --> Return top of the stack 101, stack becomes []
    customStack.pop();                            // return -1 --> Stack is empty return -1.

Constraints:

- `1 <= maxSize <= 1000`
- `1 <= x <= 1000`
- `1 <= k <= 1000`
- `0 <= val <= 100`
- At most `1000` calls will be made to each method of `increment`, `push` and `pop` each separately.