One block is needed to make an up-and-down staircase, with one step up and one step down.

$4$ blocks make an up-and-down staircase with $2$ steps up and $2$ steps down.

How many blocks would be needed to build an up-and-down staircase with $5$ steps up and $5$ steps down?

Explain how you would work out the number of blocks needed to build a staircase with any number of steps.