Have you learned something about segment tree? If not, don’t worry, I will explain it for you.
Segment Tree is a kind of binary tree, it can be defined as this:
- For each node u in Segment Tree, u has two values: Lu and Ru.
- If Lu=Ru, u is a leaf node. 
- If Lu≠Ru, u has two children x and y,with Lx=Lu,Rx=?Lu+Ru2?,Ly=?Lu+Ru2?+1,Ry=Ru.
Here is an example of segment tree to do range query of sum.



Given two integers L and R, Your task is to find the minimum non-negative n satisfy that: A Segment Tree with root node‘s value Lroot=0 and Rroot=ncontains a node u with Lu=L and Ru=R.

The input consists of several test cases. 
Each test case contains two integers L and R, as described above.
0≤L≤R≤109
LR?L+1≤2015

For each test, output one line contains one integer. If there is no such n, just output -1.

6 7
10 13
10 11

7
-1
12

2015 Multi-University Training Contest 3

题意：

给定区间[l,r]

用线段树的递归建树方式build(1, n)

问最小的n是多少，使得build(1,n) 中能直接建出区间[l,r]

思路：

注意一下范围，然后推算一下就能发现这个区间距离根节点的距离不超过10

所以从底向上搜就好了