What if there are odd number of nodes?
For example:
L: L0
What's the result?
L: L0 -> L0?
If your number of nodes is n, and you want to split the list into two halves in which the second half contains all the nodes that need to be inserted, then your second half should contain (n -1)/2 number of nodes.
This formula covers both the old number and even number cases. In the example of 4 nodes, you only need to insert one node on the tail. In the example of 5 nodes, you need to move the last 2 nodes. And so on so forth.