Insert and Remove at a Position

Both methods share one invariant: to change a link you must be standing on the node BEFORE the target, because a singly linked node cannot see backwards.

Requirements:
1. insertAt(int index, int value) puts a new node at that 0-based position and returns true; it returns false and changes nothing when index is negative or greater than size().
2. removeAt(int index) unlinks the node at that position and returns its value, or -1 when index is negative or not less than size().
3. Index 0 means the head in both methods.

The Node class is provided - do not rename it and do not add public to it, because a Java source file may contain only one public class.

Do NOT write a main method.