Given the head of a singly linked list, return the middle node of the linked list. If the number of nodes in the linked list is even, there will be two middle nodes, so return the second one.

Constraints:

Let n be the number of nodes in a linked list.

• $1 \leq$ n $\leq 100$
• $1 \leq$ Node.value $\leq 100$
• head $\neq$ NULL