#include<stdio.h>
int n,k,i,j;

long long c[27][27];

int main()
{
   freopen("sandokan.in","r",stdin);
   freopen("sandokan.out","w",stdout);
   scanf("%d %d",&n,&k);
   c[0][1]=1;
   n--;k--;
   for(i=1;i<=n;++i)
	for(j=1;j<=k;j++)
		c[i][j]=c[i-1][j-1]+c[i-1][j];
   printf("%lld",c[n-1][k-1]);
   return 0;
}