#include <algorithm>
#include <iostream>
#include <math.h>
using namespace std;
bool pan[10000001] = { 0 };
int su[100001] = { 0 };
bool zhi[100001] = { 0 };
int main()
{
    int begn, ends;
    int now = 0;
    cin >> begn >> ends;
    if(begn<2){
        begn=2;
    }
    //cout << begn << ";" << ends << endl;
    int len = sqrt(ends);
    for (int i = 2; i <= len; i++) {
        //cout << i << "/";
        if (zhi[i] == 0) {
            su[++now] = i;
        }
        for (int j = 1; j <= now && i * su[j]<= len; j++) {
            zhi[i * su[j]] = 1;
            if (i % su[j] == 0) {
                break;
            }
        }
    }
    for (int u = 1; u <= now; u++) {
        int i = su[u];
        //cout << i << " ";
        for (int j = ends / i; i * j >= begn && j != 1; j--) {
            pan[i * j - begn] = 1;
        }
    }
    int ans = 0;
    for (int i = 0; i <= ends - begn; i++) {
        if (pan[i] == 0) {
            ans++;
            //cout<<begn+i<<" ";
        }
    }
    cout << ans;
}