E-Value In Blast

Hi all:

I am calculating my e-Value for my own BLAST alignment.

I used the formulae: e= mn2^-S'

where: m = length of the query sequence n = total number of lengths of all template sequences in the template file S' = bit score.

I was wondering about parameter n: Do I need to sum all lengths of template sequences which are involved in the alignments or do I need to sum all lengths of _all_ template sequences and it doesn't matter if they are in the alignment involved or not?

Thanks!!