# N20だからビット全探索するか、前半数列と後半数列に分ける

N, K = map(int, input().split())

ans = 0
for bit in range(1<<N):
    if bit == 0 or bit == 2**N-1:
        continue
    former = []
    latter = []
    for shift in range(N):
        if bit>>shift&1 == 1:
            former.append(shift+1)
        else:
            latter.append(shift+1)
    if former[0]==K and former[-1]>latter[0]:
        ans += 1
        #print('former', former, 'latter', latter)
print(ans)