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 109 + 7. Keep in mind that dogs and monkeys are different.

Input

Two integers n and m (1 ≤ n, m ≤ 105).

Output

Print the number of different ways to arrange monkeys and dogs modulo 109 + 7.