// https://old.yosupo.jp/submission/53928
#include <cassert>
#include <cmath>
#include <cstdio>
#include <vector>

using namespace std;

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;
}

// int main() {
//   i64 N;
//   while (~scanf("%lld", &N)) {
//     printf("%lld\n", prime_pi(N));
//   }
// }
// ================================================================================

int main() {
    i64 l, r;
    scanf("%lld %lld", &l, &r);
    i64 ans =
        prime_pi(r) - prime_pi(l - 1) + prime_pi(r + r - 1) - prime_pi(l + l);
    printf("%lld\n", ans);
}