def get():
    return list(map(int, input().strip().split(' ')))

N, K = get()

def counting(n, k):
    s = [[k, k]]
    count = 0
    while len(s) > 0:
        x, y = s.pop()
        if y <= n:
            count += 1
            s.append([x, y + 1])
            s.append([y + 1, y + 1])
        elif x < n:
            s.append([x + 1, x + 1])
    return count

count = counting(N, K)
                 
print(count)