#include<stdio.h>

int n,k,i;
long long x=1,y=1;

int main()
{
   freopen("sandokan.in","r",stdin);
   freopen("sandokan.out","w",stdout);
   scanf("%d %d",&n,&k);
   for(i=k+1;i<n;i++)
	x*=i;
   for(i=2;i<n-k;i++)
	y*=i;
   x/=y;
   printf("%lld",x);
   return 0;
}