n, k = map(int, input().split())

if k == 1:
    if n == 1:
        print(0)
    else:
        part1 = (2 ** (n - 2) - 1) if (n >= 2) else 0
        part2 = 0
        m = n - 2  # number of elements from 3 to n
        if m > 0:
            possible = set(range(3, n + 1))
            for mask in range(1, 1 << m):  # exclude empty subset
                elements = []
                for i in range(m):
                    if (mask >> i) & 1:
                        elements.append(3 + i)
                s_set = set(elements)
                remaining = possible - s_set
                if remaining:
                    x = min(remaining)
                else:
                    x = n + 1  # larger than any possible max_sd
                max_sd = max(elements)
                if max_sd > x:
                    part2 += 1
        print(part1 + part2)
else:
    if k > n:
        print(0)
    else:
        ans = 1 << (n - k)
        print(ans)