Could u please give Idea and code for this Question

using the following script we do the data driven test, data 
from flat file i.e., from notepad, Ms-Word etc.,
option explicit
dim fso,f,n
set fso=createobject("Scripting.filesystemobject")
set f=fso.opentextfile("path of word doc.",1,false)
while(f.atendofline<>true)'read the file to the end  of file
n=f.readline()'line by line reading

In Case, if my word or text file is having millions of 
lines then how can i calculate efficiently the total number 
of lines?