N = 1000100
isprime = [True] * N
isprime[0] = isprime[1] = False
for i in range(2, int(N ** 0.5 + 1)):
    if not isprime[i]:
        continue
    for j in range(i * i, N, i):
        isprime[j] = False

n, p = map(int, input().split())
for i in range(2, int(p ** 0.5 + 1)):
    if p % i == 0:
        p = i
        break
    
if 2 * p <= n:
    ans = n - sum(isprime[n // 2 + 1:n + 1]) - 1
    print(ans)
else:
    print(1)