def primes(n):
    is_prime = [True] * (n + 1)
    is_prime[0] = False
    is_prime[1] = False
    for i in range(2, int(n ** 0.5) + 1):
        if not is_prime[i]:
            continue
        for j in range(i * 2, n + 1, i):
            is_prime[j] = False
    return (i for i in range(n + 1) if is_prime[i])


N, P = map(int, input().split())
pr = set(primes(N))
if P in pr and P * 2 > N:
    ans = 1
else:
    ans = N - 1 - sum(p * 2 > N for p in pr)
print(ans)