#yuki826
import sys

n,p=map(int,raw_input().split())
if p==1:
 res=1
 sys.exit()
res=n-1
for i in range(n/2+1,n+1):
 f=True
 j=2
 while j*j<=i:
  if i%j==0:
   f=False
   break
  else:
   j+=1
 if f:
  res-=1
  if i==p:
   res=1
   break
print res