Excel Formula needed!

I am counting if a range of cells containing “a”
Thanks to some previous help I arrived at this formula: countif(d14:ah15,”a”)
This works. However, I need the total to be divided by 2. I have used extra brackets etc to no avail.Ex. countif((d4:ah15)/2,”a”). What is wrong with that formula so that I can fix it and arrive at half the total.
Thanks
Merv