Description

There are $r$ distinct boxes and $n$ distinct balls. Put these $n$ balls into the $r$ boxes, with no box left empty. Find how many different placements there are.

Two placements are different if and only if there exists a ball that is placed into different boxes in the two placements.

Input Format

The input contains one line with two integers, representing $n$ and $r$.

Output Format

Output one line with a single integer representing the answer.

3 2

6

Hint

Sample Explanation 1

There are two boxes (IDs $1, 2$) and three balls (IDs $1, 2, 3$), for a total of six arrangements, as follows:

Constraints

For $100\%$ of the testdata, it is guaranteed that $0 \leq r \leq n \leq 10$, and the answer is less than $2^{31}$.

Translated by ChatGPT 5