#include<stdio.h>
int main()
{int i,j,n,m;
FILE *fin,*fout;
    fin=fopen("nucle.in","rb");
	fout=fopen("nucle.out","wb");
	fscanf(fin,"%d%d",&n,&m);
	int all=0;
	for(i=1;i<=n;i++)
	{
		int t=n;
		for(j=n-1;j>=n-i+1;j--)
			t=t*j;
		for(j=i;j>=2;j--)
			t=t/j;
		all=all+t;
	}
	for(i=m+1;i<=n;i++)
		if(i!=2&&i!=1)all=all-(n-i+1)*(n-i+1);
	else all=all-(n-i+1);
	if(m==1||m==0)fprintf(fout,"%d",m);
	else if(n==0)fprintf(fout,"0");
	else fprintf(fout,"%d",all+1-(n-m+1));
	fclose(fin);
	fclose(fout);
	return 0;
}