#include <bits/stdc++.h>
using namespace std;

//Counting Primes
//https://judge.yosupo.jp/submission/53928 より
using i64 = long long;

int isqrt(i64 n) {
  return sqrtl(n);
}

__attribute__((target("avx2"), optimize("O3", "unroll-loops")))
i64 prime_pi(const i64 N) {
  if (N <= 1) return 0;
  if (N == 2) return 1;
  const int v = isqrt(N);
  int s = (v + 1) / 2;
  vector<int> smalls(s); for (int i = 1; i < s; ++i) smalls[i] = i;
  vector<int> roughs(s); for (int i = 0; i < s; ++i) roughs[i] = 2 * i + 1;
  vector<i64> larges(s); for (int i = 0; i < s; ++i) larges[i] = (N / (2 * i + 1) - 1) / 2;
  vector<bool> skip(v + 1);
  const auto divide = [] (i64 n, i64 d) -> int { return double(n) / d; };
  const auto half = [] (int n) -> int { return (n - 1) >> 1; };
  int pc = 0;
  for (int p = 3; p <= v; p += 2) if (!skip[p]) {
    int q = p * p;
    if (i64(q) * q > N) break;
    skip[p] = true;
    for (int i = q; i <= v; i += 2 * p) skip[i] = true;
    int ns = 0;
    for (int k = 0; k < s; ++k) {
      int i = roughs[k];
      if (skip[i]) continue;
      i64 d = i64(i) * p;
      larges[ns] = larges[k] - (d <= v ? larges[smalls[d >> 1] - pc] : smalls[half(divide(N, d))]) + pc;
      roughs[ns++] = i;
    }
    s = ns;
    for (int i = half(v), j = ((v / p) - 1) | 1; j >= p; j -= 2) {
      int c = smalls[j >> 1] - pc;
      for (int e = (j * p) >> 1; i >= e; --i) smalls[i] -= c;
    }
    ++pc;
  }
  larges[0] += i64(s + 2 * (pc - 1)) * (s - 1) / 2;
  for (int k = 1; k < s; ++k) larges[0] -= larges[k];
  for (int l = 1; l < s; ++l) {
    int q = roughs[l];
    i64 M = N / q;
    int e = smalls[half(M / q)] - pc;
    if (e < l + 1) break;
    i64 t = 0;
    for (int k = l + 1; k <= e; ++k) t += smalls[half(divide(M, roughs[k]))];
    larges[0] += t - i64(e - l) * (pc + l - 1);
  }
  return larges[0] + 1;
}
//ここまで

signed main(){

    long long L, R; cin >> L >> R;
    long long ans = prime_pi(R) - prime_pi(L - 1);
    if(L < R){
        ans += prime_pi(2 * R - 1) - prime_pi(2 * L - 1);
        if(2 * L - 1 < 2) ans--;
    }
    cout << ans << endl;

    return 0;
}