import sequtils,math,times
template stopwatch(body) = (let t1 = cpuTime();body;stderr.writeLine "TIME:",(cpuTime() - t1) * 1000,"ms")
template times*(n:int,body) = (for _ in 0..<n: body)
template `max=`*(x,y) = x = max(x,y)
template `min=`*(x,y) = x = min(x,y)
proc getchar_unlocked():char {. importc:"getchar_unlocked",header: "<stdio.h>" ,discardable.}
proc scan(): int =
  while true:
    let k = getchar_unlocked()
    if k < '0': return
    result = 10 * result + k.ord - '0'.ord
#[
template useUnionFind() = # 同一集合の判定/マージ が 実質 O(1)
  type UnionFind[T] = ref object
    parent : seq[T]
  proc newUnionFind[T](size:int) : UnionFind[T] =
    new(result)
    result.parent = newSeqUninitialized[T](size)
    for i in 0.int32..<size.int32: result.parent[i] = i
  proc root[T](self:var UnionFind[T],x:T): T =
    if self.parent[x] == x: return x
    self.parent[x] = self.root(self.parent[x])
    return self.parent[x]
  proc same[T](self:var UnionFind[T],x,y:T) : bool = self.root(x) == self.root(y)
  proc merge[T](self:var UnionFind[T],sx,sy:T) : bool {.discardable.} =
    var rx = self.root(sx)
    var ry = self.root(sy)
    if rx == ry : return false
    if self.parent[ry] < self.parent[rx] : swap(rx,ry)
    if self.parent[rx] == self.parent[ry] : self.parent[rx] -= 1
    self.parent[ry] = rx
    return true
  proc count[T](self:var UnionFind[T],x:T):int =
    for p in self.parent:(if p == self.parent[x]: result += 1)
useUnionFind()

stopwatch:
  let n = scan()
  let p = scan()
  var F = newUnionFind[int](n+1)
  var notIsPrimes = newSeq[bool](n+1)
  stopwatch:
    for i in 2..n.float.sqrt.int:
      if notIsPrimes[i] : continue
      for j in countup(i*2,n,i):
        F.merge(i,j)
        notIsPrimes[j] = true
  for i in n.float.sqrt.int..n div 2:
    if notIsPrimes[i]: continue
    F.merge(2,i)
  echo F.parent
  # echo F.parent[p]
  stopwatch:
    echo F.count(p)
]#
# 結果を見て、0,1,[2....]
let n = scan()
let p = scan()
if p == 1 : quit "1",0
var isNotPrimes : array[100_0010,bool]
stopwatch:
  for i in countup(2,n.float.sqrt.int):
    if isNotPrimes[i]:continue
    for j in countup(2*i,n,i):
      isNotPrimes[j] = true
  if p >= n div 2 and not isNotPrimes[p]:
    quit "1",0
stopwatch:
  var ans = n div 2 - 1
  for i in countup(n div 2 + 1,n):
    if isNotPrimes[i] : ans += 1
  echo ans