Nesting Dolls#2770
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Nesting Dolls

0.5 seconds
64 megabytes
Very easy

There are nesting dolls of different sizes on the table. A smaller nesting doll can be placed inside a larger one, which in turn can be placed inside an even larger one, and so on.

In how many ways can you nest some of the dolls so that exactly nesting dolls remain on the table?

Input

The input consists of two integers and (1 \leq K \leq N \leq 12).

Output

Output a single integer — the desired number of ways.

Examples

Example 1

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