n, k = map(int,input().split())
if k == 1:
    if n == 2:
        ans = 0
    elif n == 3:
        ans = 1
    elif n == 4:
        ans = 4

    else:
        ans = 0
        for i in range(n - 1):
            #print(i)
            if i == n - 2:
                ans += 2 ** (i - 1)
            else:
                ans += 2 ** i
            
else:
    ans = 2 ** (n - k)

print(ans)