/**
*Prob	: k
*Data	: 2012-11-8
*Sol	: 递推
*/

/* For ( 刘畅，彭博，程志博 三个魂淡) */

#include <iostream>
#include <cstdio>
#include <cstring>

#define lld long long

#define MaxN 30

using namespace std;

int n,k;
lld f[MaxN][MaxN];

int main()
{
	freopen("k.in","r",stdin);
	freopen("k.out","w",stdout);
	
	scanf("%d%d",&n,&k);

	for (int i=1; i<=n; i++)
		f[i][i] = 1;
	
	for (int i=2; i<=n; i++)
		for (int j=1; j<=k; j++)
			f[i][j] = f[i-1][j-1]*(i-j+1) + f[i-1][j]*j;

	cout<<f[n][k]<<endl;

	fclose(stdin); fclose(stdout);
	return 0;
}