#include <bits/stdc++.h>
#define ft first
#define sc second
#define lb lower_bound
#define ub upper_bound
#define pb push_back
#define pt(sth) cout << sth << "\n"
#define chmax(a, b) {if(a<b) a=b;}
#define chmin(a, b) {if(a>b) a=b;}
#define moC(a, s, b) (a)=((a)s(b)+MOD)%MOD
using namespace std;
typedef long long ll;
typedef pair<ll, ll> P;
static const ll INF=1e18;
static const ll MAX=1e5+7;
static const ll MOD=1e9+7;
ll max(ll a, ll b) {return a>b?a:b;}
ll min(ll a, ll b) {return a<b?a:b;}

int main(void) {
  ll N, P;
  cin >> N >> P;
  ll i, j;
  
  ll p[MAX*10];
  memset(p, 1, sizeof(p));
  p[0]=p[1]=0;
  for(i=2; i*i<=N; i++) {
    if(p[i]==0) continue;
    for(j=i+i; j<=N; j+=i) {
      p[j]=0;
    }
  }
  
  if(p[P]&&P*2>N) pt(1);
  else {
    ll ans=N-1;
    for(i=0; i<=N; i++) {
      if(p[i]&&i*2>N) {
        ans--;
      }
    }
    
    pt(ans);
  }
  
}