题目描述
Snuke has N dogs and M monkeys. He wants them to line up in a row.
As a Japanese saying goes, these dogs and monkeys are on bad terms. ("ken'en no naka", literally "the relationship of dogs and monkeys", means a relationship of mutual hatred.) Snuke is trying to reconsile them, by arranging the animals so that there are neither two adjacent dogs nor two adjacent monkeys.
How many such arrangements there are? Find the count modulo 10^9+7 (since animals cannot understand numbers larger than that). Here, dogs and monkeys are both distinguishable. Also, two arrangements that result from reversing each other are distinguished.
Constraints
- 1 ≤ N,M ≤ 10^5
Input
Input is given from Standard Input in the following format:
N M
Output
Print the number of possible arrangements, modulo 10^9+7.
Examples
Input
2 2
Output
8
Input
3 2
Output
12
Input
1 8
Output
0
Input
100000 100000
Output
530123477
输入格式
见题面
输出格式
见题面