#include<bits/stdc++.h>
using namespace std;
int a[1000010];
int b[1000010]={1,1}; 

int main(){
    int m,n,ans=0,sum=0;
    cin>>m>>n;
    for(int i=2;i<=n;i++){
        if(b[i]==0){ 
            a[ans++]=i;
            if(i>=m) sum++; 
        }
        for(int j=0;j<ans;j++){
            if(a[j]*i<=n){
                b[a[j]*i]=1; 
            }else break;
            if(i%a[j]==0) break; 
        }
    }
    cout<<sum;
    return 0;
}
/**************************************************************
	Problem: 1063
	User: tangkaixuan
	Language: C++
	Result: Accepted
	Time:8 ms
	Memory:9884 kb
****************************************************************/