Cant recall the exact points for hidan - is it 55? 1 key for me gave about 3.5-3.8 points per? (you c*ways test and see how ur luck is holding).
at 55 points per frag you need 4400 total, if you assume 3.5 per key its 1257 keys, 3.8 is 1158, or you can just do your own math with what you see