import sys
read = sys.stdin.buffer.read
readline = sys.stdin.buffer.readline
readlines = sys.stdin.buffer.readlines

import numpy as np

N, P = map(int, read().split())

U = N + 1
is_prime = np.zeros(U, np.bool)
is_prime[2] = 1
is_prime[3::2] = 1
for p in range(3, U, 2):
    if p * p >= U:
        break
    if is_prime[p]:
        is_prime[p*p::p+p] = 0

M = N // 2 + 1

n_single = np.count_nonzero(is_prime[M:]) + 1
if P == 1 or (P >= M and is_prime[P]):
    answer = 1
else:
    answer = N - n_single

print(answer)