I have a formula $x=\frac{1}{\frac{Y}{1000}}$ which is the calculation for converting Parallax to Parsec. I need to reverse it but can't remember how to reverse $1/$ .

So for a Parallax of $49.56$, divide by $1000$ then divide $1$ by $0.04956$ equals $20.17756$.

If I have $20.17756$, how do i get back to $49.56$ via $0.04956$.

I am looking for a simple explanation, one that can be calculated in a non-scientific calculator.

Thanks.