#include <algorithm>
#include <cassert>
#include <cmath>
#include <functional>
#include <iomanip>
#include <iostream>
#include <map>
#include <numeric>
#include <queue>
#include <set>
#include <tuple>
#include <vector>

#define debug_value(x) cerr << "line" << __LINE__ << ":<" << __func__ << ">:" << #x << "=" << x << endl;
#define debug(x) cerr << "line" << __LINE__ << ":<" << __func__ << ">:" << x << endl;

template <class T>
inline bool chmax(T& a, T b) {
    if (a < b) {
        a = b;
        return 1;
    }
    return 0;
}
template <class T>
inline bool chmin(T& a, T b) {
    if (a > b) {
        a = b;
        return 1;
    }
    return 0;
}

using namespace std;
typedef long long ll;

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

ll prime_pi(const ll 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<ll> 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 = [](ll n, ll 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 (ll(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;
                ll d = ll(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] += ll(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];
        ll M = N / q;
        int e = smalls[half(M / q)] - pc;
        if (e < l + 1) break;
        ll t = 0;
        for (int k = l + 1; k <= e; ++k) t += smalls[half(divide(M, roughs[k]))];
        larges[0] += t - ll(e - l) * (pc + l - 1);
    }
    return larges[0] + 1;
}

int main() {
    ios::sync_with_stdio(false);
    cin.tie(0);
    cout << setprecision(10) << fixed;
    ll l, r; cin >> l >> r;
    if(l == 1 && r == 1){
        cout << 0 << endl;
        return 0;
    }
    ll ans = prime_pi(r)-prime_pi(l-1);
    ans += prime_pi(r*2-1)-prime_pi(l*2);
    cout << ans << endl;
}