#include <bits/stdc++.h>
using namespace std;
const int INF = 0x3f3f3f3f, N = 2e6 + 5, MOD = 998244353;
const long long INF_LL = 0x3f3f3f3f3f3f3f3fLL;
template <typename T>
inline int getplc(T x, int y) {
  return (x >> y) & 1;
}
template <typename T>
T square(T x) {
  return x * x;
}
long long qpow(long long a, long long b = MOD - 2, long long _MOD = MOD) {
  if (a == 0) return a;
  long long res = 1;
  for (; b; b >>= 1, a = a * a % _MOD) {
    if (b & 1) res = res * a % _MOD;
  }
  return res;
}
template <typename T>
T Smax(T x) {
  return x;
}
template <typename T, typename... Args>
T Smax(T a, Args... args) {
  return max(a, Smax(args...));
}
template <typename T>
T Smin(T x) {
  return x;
}
template <typename T, typename... Args>
T Smin(T a, Args... args) {
  return min(a, Smin(args...));
}
template <typename T>
void errl(istream_iterator<string> it) {}
template <typename T, typename... Args>
void errl(istream_iterator<string> it, T a, Args... args) {
  cerr << *it << " = " << a << endl;
  errl(++it, args...);
}
void err(istream_iterator<string> it) {}
template <typename T, typename... Args>
void err(istream_iterator<string> it, T a, Args... args) {
  cerr << *it << "=" << a << " # ";
  err(++it, args...);
}
int prime[20000005], ss;
bitset<(int)3e8 + 5> isprime;
void work(int maxn) {
  for (int i = 2; i <= maxn; i++) {
    if (!isprime[i]) {
      prime[++ss] = i;
    }
    for (int j = 1; j <= ss && prime[j] * i <= maxn; j++) {
      isprime[prime[j] * i] = 1;
      if (!(i % prime[j])) break;
    }
  }
}
void Solve() {
  int l, r, ans = 0;
  cin >> l >> r;
  work(r);
  for (int i = 5; i <= r; i += 4) {
    if (i >= l && !isprime[i]) ans++;
  }
  if (l <= 2 && 2 <= r) ans++;
  cout << ans << endl;
}
int main() {
  ios::sync_with_stdio(false);
  cin.tie(0), cout.tie(0);
  Solve();
  return 0;
}
