Circular Coloring

Bobo considers $(n + m)$ balls arranged in a circle.
The balls are numbered with $0, 1, \dots, (n + m - 1)$ where the ball $i$ and the ball $(i + 1) \bmod (n + m)$ are adjacent.

Bobo would like to color $n$ of his balls black and $m$ of his balls white.
Bobo groups adjacent balls with same colors, and he determines the weight of the coloring as the product of the lengths of groups.

He would like to know the sum of the weight of the possible colorings, modulo $(10^9+7)$.

The input consists of several test cases and is terminated by end-of-file.

Each test case contains two integers $n$ and $m$.

For each test case, print an integer which denotes the result.

## Constraint

* $1 \leq n, m \leq 5000$
* The number of test cases does not exceed $5000$.

1 2
2 3
5000 5000

6
40
975597525

For the second sample, there are $10$ possible colorings (listed below).
The number followed is the corresponding weight.

* `BBWWW` ($6$)
* `BWBWW` ($2$)
* `BWWBW` ($2$)
* `BWWWB` ($6$)
* `WBBWW` ($6$)
* `WBWBW` ($2$)
* `WBWWB` ($2$)
* `WWBBW` ($6$)
* `WWBWB` ($2$)
* `WWWBB` ($6$)

CCPC2018-湖南全国邀请赛-重现赛（感谢湘潭大学）