#include <iostream>
#define int unsigned long long
using namespace std;
signed main()
{
	int n,m,t=0;
	cin>>m>>n;
	int prime[1000000];
	for(int i = m;i <= n;i++) prime[i] = true;
	prime[1]=false;
	for(int i = m;i*i<= n;i++){
	    if(prime[i])
	        for(int j = m;j<= n/i;j++)
	            prime[j * i] = false;
	}
	for(int i = m;i<= n;i++){
		if(prime[i]){
	    	t++;
		}
	}
	cout<<t;
	return 0;
}