Competitions
Комбинаторика. Формула
Dogs and monkeys
Barish has n dogs and m monkeys. He wants to line them up. But he doesn't want to put two dogs or two monkeys together, because in this case they start to fight. How many different arrangements exists, such that neither the monkeys nor the dogs fight. Print the answer modulo 10^9 + 7. Keep in mind that dogs and monkeys are different.
Input data
Two integers n and m (1 ≤ n, m ≤ 10^5).
Output data
Print the number of different ways to arrange monkeys and dogs modulo 10^9 + 7.
Examples
Input example #1
2 2
Output example #1
8
Input example #2
3 2
Output example #2
12
Input example #3
1 8
Output example #3
0