Variable Pop-Up

Hello guys,

I want to display a pop up at the opening of a query.

In this pop up user can choose a number N (a variable) : it's a number of days.

I want to use this number N chosen by user in another variable X which is in a selection S. I would fill this variable X by formula : Actual Date - N.

But i don't know how to do.

User must choose a number of days which will be used in a variable in a selection !

I hope you could help me.

Best cheers,

Vince.