#include<iostream>
using namespace std;
int main(){
	int a,b,count=0,shu=0;
	cin>>a>>b;
	for(a;a<=b;a++){
		for(int n=2;n<a;n++){
			if(a%n==0){
				shu++;
			}
		}
		if(shu!=0){
			count++;
		}
	}
	cout<<count;
	return 0;
}