I have a damaged Surface Pro 3 and the keyboard that goes with. I am looking at upgrading to a Surface Pro 4 rather than paying to have the 3 repaired. Will my existing keyboard (kb) bwork with a 4 or will I need to buy a new kb as well? I know there are some improvements made to the 4 kb but that $150 busts my budget so I would like to use my 3 kb for a while if I can.