#include<bits/stdc++.h>
using namespace std;

// 创建一个布尔数组长度和N相同，默认值为false
bool signs[5000001];
long long s,e,i,j,c;

int main() {

	
    cin>>s>>e;
    // 计数变量
    signs[0] = true;
    signs[1] = true;
    for (i = 2; i <= e; i++) {
        if (signs[i]==false) {
            for (j = i*2; j<=e; j = j+i) {
                signs[j] = true;
            }
        }
    }
    for(i=2; i<e; i++) {
        if(signs[i]==false) {
            for(j=i; i*j<=e; j++) {
                if(i*j >= s &&signs[j]==false) {
                    c++;
                }
            }
        }
    }
    cout<<c;

	return 0;
}

/**************************************************************
	Problem: 2007
	User: admin
	Language: C++
	Result: Accepted
	Time:916 ms
	Memory:6956 kb
****************************************************************/