Partition Into Subsets

easy
1. You are given a number n, representing the number of elements.
2. You are given a number k, representing the number of subsets.
3. You are required to print the number of ways in which these elements can be partitioned in k non-empty subsets.
E.g.
For n = 4 and k = 3 total ways is 6
12-3-4
1-23-4
13-2-4
14-2-3
1-24-3
1-2-34

Input Format

A number n A number k

Output Format

A number representing the number of ways in which these elements can be partitioned in k non-empty subsets.

Constraints

0 <= n <= 20
0 <= k <= n

Notice

Try First, Check Solution later

1. You should first read the question and watch the question video.
2. Think of a solution approach, then try and submit the question on editor tab.
3. We strongly advise you to watch the solution video for prescribed approach.

Example

Input
4
3
Output
6
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