#include <bits/stdc++.h>   using namespace std;   const int size = 300000001;   bitset<size> gut;   int main() {     int l, r;     cin >> l >> r;     gut.set();     for (int i = 3; i * i <= r; i += 2) {       if (gut[i])         for (int j = i * i; j <= r; j += (i << 1)) {           gut[j] = false;         }     }     int rez = 0;     rez = (l <= 2 && r >= 2);     for (int i = 5; i <= r; i += 4) {       if (i >= l && gut[i]) rez++;     }     cout << rez << endl;     return 0;   }   