N,K=map(int,input().split())
a=0
for i in range(1,(1<<N)-1):
	b=[j+1 for j in range(N)if((i>>j)&1)]
	c=[j+1 for j in range(N)if not((i>>j)&1)]
	if min(b)==K and max(b)>min(c):
		a+=1
print(a)