#include <cassert>
#include <cmath>
#include <algorithm>
#include <iostream>
#include <iomanip>
#include <limits.h>
#include <map>
#include <queue>
#include <string.h>
#include <vector>

using namespace std;
typedef long long ll;

class Prime {
public:
  vector<ll> prime_list;
  const ll MAX_N = 2000010;

  Prime() {
    bool checked[MAX_N + 1];
    memset(checked, false, sizeof(checked));

    for (ll i = 2; i <= MAX_N; ++i) {
      if (!checked[i]) {
        prime_list.push_back(i);

        for (ll j = i * i; j <= MAX_N; j += i) {
          checked[j] = true;
        }
      }
    }
  }

  map<ll, int> prime_division(ll n) {
    map<ll, int> res;

    for (ll i = 0; prime_list[i] <= sqrt(n); ++i) {
      ll p = prime_list[i];

      while (n % p == 0) {
        ++res[p];
        n /= p;
      }
    }

    if (n != 1) {
      res[n] = 1;
    }

    return res;
  }

  bool is_prime(ll n) {
    if (n <= 1) return false;

    for (int i = 0; i < prime_list.size(); ++i) {
      if (n % prime_list[i]) return false;
    }

    return true;
  }
};

int main() {
  int L, R;
  cin >> L >> R;
  Prime prime;

  int ans = 0;
  for (int x : prime.prime_list) {
    if (x < L) continue;
    if (x > 2 * R) break;

    if (x <= R) ans++;
    if (x > 2 && x / 2 >= L) ans++;
  }

  cout << ans << endl;

  return 0;
}