Given a linked list, find its middle element.
Definition of a single linked list:
Implement a function MiddleElement that returns a pointer to the middle node. If linked list contains n elements, its middle element has index number ceil(n / 2).
The length of the list n = 5 is odd. Function MiddleElement must return a pointer to the node with value 3 (middle element).
The length of the list n = 4 is even. Function MiddleElement must return a pointer to the node with value 2 (middle element).