1st element is a query for value 6, as Fenwick tree is empty -> result is 0
  2nd is element 5 -> add index 0 into Fenwick tree
  3rd element is 4 -> add index 1 into tree.
  4th element is 3 -> add index 4 into tree.
  5th element is 2 -> add index 2 into tree.
  6th element is query for range (2, 5), we query the tree and get answer 2.
  7th element is 1 -> add index 3 into tree.
  Finish.

count = m-j;

i=0; for (j=1;j<=m;j<<=1;); j>>=1;

[9   4   5   6   1   3   2   8] Node 1
[9   4   5   6] [1   3   2   8] Node 2-3
[9   4] [5   6] [1   3] [2   8] Node 4-7
[9] [4] [5] [6] [1] [3] [2] [8] Node 8-15

[1   2   3   4   5   6   8   9] Node 1
[4   5   6   9] [1   2   3   8] Node 2-3
[4   9] [5   6] [1   3] [2   8] Node 4-7
[9] [4] [5] [6] [1] [3] [2] [8] Node 8-15