#include <bits/stdc++.h>   using namespace std;   const int MAXN = 300000000 + 10;   bitset<MAXN> check;   void Get_prime(int n) {     check.set();     check[0] = check[1] = 0;     for (int i = 2; i <= sqrt(n + 0.5); ++i) {       if (check[i])         for (int j = 2; i * j <= n; ++j) check[i * j] = 0;     }   }   int main() {     ios::sync_with_stdio(false);     cin.tie(0);     int l, r;     cin >> l >> r;     Get_prime(r);     int cnt = 0, i;     if (l <= 2 && 2 <= r) ++cnt;     if (l % 4 <= 1)       i = l / 4 * 4 + 1;     else       i = (l / 4 + 1) * 4 + 1;     for (i; i <= r; i += 4)       if (check[i]) ++cnt;     cout << cnt;   }   