#include <iostream>
#include <cmath>
using namespace std;


int main()
{
	 int n, m;	
	 const int MAXN = 10000001;
	 bool simple[MAXN];
	 for(int i = 2; i <= MAXN; i++){
	     simple[i] = true;
	 }
	 for(int i = 2; i <= sqrt(MAXN); i++){
	     if(simple[i]){
	         for(int j = i * i; j <= MAXN; j += i){
	             simple[j] = false;
	         }
	     }
	 }

	 int count[MAXN];
	 int lastSum = 0;
	 for(int i = 1; i < MAXN; i++){
	     count[i] = lastSum + simple[i];
	     lastSum = count[i];
	 }
	 while(cin >> m >> n){
	     int answer = count[n] - count[m] + simple[m];
	     cout << answer << endl << endl;
	 }
}