Limits: 1s, 512 MB

A common example of recursion goes something like this:

It is of course easy to calculate the value of this function for any **x** when the values of **X0** and **X1** are known. However, your task is to find the value of recur for a given number without being given the values of **X0** and **X1**. Instead, you are given the values of **recur(a)** and **recur(b)** for given values of **a** and **b**.

This is a companion discussion topic for the original entry at https://toph.co/p/recursive-function