Problem Description

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.

 

Input

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

 

Output

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

 

Sample Input

6 7

10 13

10 11

 

Sample Output

7

-1

12

 

Source

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