Sac I fragments - how many 4.5Kb fragments??? (Sep/10/2003 )

I need to clone a 4.5 Kb DNA fragment of total genomic DNA after SacI digestion (containing a translocation i wanna characterize)...how can i know how many different 4.5Kb DNA fragments are present in the total genomic DNA i digested? (just to know how many different clones i'll have to screen to find my particular one..)
i thank you for your kind help

....it's human total genomic DNA what we are asking about....
thanks