Calculating points for lists of films

I can't seem to work out an easy way to do this. We are collecting lists of favourite films from some forum members (at least 30 people so far). The lists can be any length, but the point system is 1000 for #1, 1 for #1000 and 0.5 for any after that. How can I calculate the number of points each film gets? I have the sheet set up so that A contains rank #, B has # points and then others are the film lists.