We now understand the definition of functions.

If , where and then is called an image of , and is called the preimage of .

Given and ,

and

We call the function as (one-to-one) if:

Let us define a particular one-to-one function as , such that

where .

The function defined in the previous challenge is not one-to-one because:

Your task is to complete the function that takes as the input and return .

Constraints