Question about flue pipe

I have my fireplace set where I want it in my new addition. Right between two windows. The flue pipe straight up will just catch a truss. I checked at the local fireplace shop today and they have a couple 30° elbows for $125..My flue is the air cooled pipe. Can any of you tell me just how far two 30° elbows will shift the pipe over? He also has two 15° elbows. How much will they shift the flue pipe?

30* can offset 2 ft offset in 4 ft distance. 15* can offset ~1 ft in 4 ft distance. What is the distance from flue exit to ceiling (or better is Ceiling Support Box)?

Only have about three or 4 feet to trusses.Guess I may just have to off center the fireplace about 5 inches to get a straight shot.

15* can offset only 5" if you go elbow-elbow or a very short pipe between elbows - gives less offset. If it's only 5" - moving FP and going straight up would be easier and cheaper.