import numpy as np


def primes_np(n):
    is_prime = np.ones(n + 1, dtype=bool)
    is_prime[0] = False
    is_prime[1] = False
    for i in range(2, int(n ** 0.5) + 1):
        if not is_prime[i]:
            continue
        is_prime[i * 2:n + 1:i] = False
    return is_prime


N, P = map(int, input().split())
pr = primes_np(N)
if pr[P] and P * 2 > N:
    ans = 1
else:
    ans = N - 1 - np.count_nonzero(pr[N // 2 + 1:])
print(ans)