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

import sys

if K == 1 and N == 2:
    print(0)
    exit()
if K == N:
    print(1)
    exit()

if K == 1:
    ans = 2 ** (N - 1) - (N - 1) - 1
    print(ans)
    exit()
u = N - K
print(2 ** u)