#include <iostream>
#include <algorithm>
#include <string>
#include <vector>
#include <cmath>
#include <map>
#include <queue>
#include <iomanip>
#include <set>
#include <tuple>
#define mkp make_pair
#define mkt make_tuple
#define rep(i,n) for(int i = 0; i < (n); ++i)
using namespace std;
typedef long long ll;
const ll MOD=1e9+7;
template<class T> void chmin(T &a,const T &b){if(a>b) a=b;}
template<class T> void chmax(T &a,const T &b){if(a<b) a=b;}

class DisjointSet{
public:
  vector<int> rank,p;
  vector<int> sz;
 
  DisjointSet(){}
  DisjointSet(int size){
    rank.resize(size,0);
    p.resize(size,0);
    sz.resize(size,0);
    for(int i=0;i<size;i++) makeSet(i);
  }
 
  void makeSet(int x){
    p[x]=x;
    rank[x]=0;
    sz[x]=1;
  }
 
  bool same(int x,int y){
    return findSet(x)==findSet(y);
  }
 
  void unite(int x,int y){
    if(same(x,y)) return;
    link(findSet(x),findSet(y));
  }
 
  void link(int x,int y){
    if(rank[x]>rank[y]){
      p[y]=x;
      sz[x]+=sz[y];
    }else{
      p[x]=y;
      sz[y]+=sz[x];
      if(rank[x]==rank[y]){
        rank[y]++;
      }
    }
  }
 
  int findSet(int x){
    if(x!=p[x]){
      p[x]=findSet(p[x]);
    }
    return p[x];
  }
 
  int findSize(int x){
    return sz[findSet(x)];
  }
};

int main(){
  cin.tie(0);
  ios::sync_with_stdio(false);

  int L,R;
  cin>>L>>R;

  vector<int> isprime(R+1,1);
  vector<ll> primes;
  for(ll i=2;i<=R;i++){
    if(isprime[i]==0) continue;
    primes.push_back(i);
    for(ll j=2;i*j<=R;j++) isprime[i*j]=0;
  }

  DisjointSet us(R+1);
  for(int i=L;i<=R;i++){
    for(int j=0;j<primes.size();j++){
      if(i*primes[j]>R) break;
      us.unite(i,i*primes[j]);
    }
  }

  int ans=0;
  for(int i=L;i<=R;i++) if(us.findSet(i)==i) ans++;
  cout<<ans-1<<endl;

  return 0;
}