The 0th and 1st Frabonacci trees are each single nodes. For all i > 1, the ith Frabonacci tree is constructed as follows:

Create a new node r. This will be the root node of the ith Frabonacci tree.

Construct the (i1)th and (i2)th Frabonacci trees.

Attach the (i2)th Frabonacci tree as the left subtree of r.

Attach the (i1)th Frabonacci tree as the right subtree of r.
The number of vertices in Frabonacci trees grows very quickly, for example there are about 4*10^10 vertices in the 50th Frabonacci tree.
To traverse a Frabonacci tree in preorder, perform the following operations:

Visit the root.

Traverse the left subtree.

Traverse the right subtree.
Let's traverse a Frabonacci tree and enumerate all vertices in the order of their visiting.
There is the 3rd Frabonacci tree with enumerated vertices on the picture.
You are given three ints n, startIndex, finishIndex. Return the shortest route between the vertices startIndex and finishIndex in form of a String in the nth Frabonacci tree. Each character of the result will be "L", "R" or "U", where "L" means a move to the left son, "R" means the move to the right son, and "U" means the move to
the parent.
