#include <stdio.h>
#include <iostream>
#include <cstring>
#include <algorithm>
using namespace std;
const int maxn = 1000000 + 5;  
int prime[maxn];  
void getprime() {  
    memset(prime, 0, sizeof(prime));  
    for (int  i = 2; i <= maxn; i++) {  
        if (!prime[i]) prime[++prime[0]] = i;  
        for (int j = 1; j <= prime[0] && prime[j] * i <= maxn; j++) {  
            prime[prime[j] * i] = 1;  
            if (i % prime[j] == 0) break;  
        }  
    }  
}
int main(){
	getprime();
	int a,b;
	while(cin >> a >>b){
	if(a > b) swap(a,b);
		int count = 0;
	for(int i = 1;i < maxn;i++){
	   if(prime[i] >=a) count++;
		if(prime[i] >b) {
			count--;
			break;			
			}
	}
	cout <<count<<endl;
	}
	return 0;
}