C++ :

#include <iostream>
using namespace std;
int main() {
int a = 0, b = 0, cnt = 0;
cin >> a >> b;
for (int n = a; n <= b; n++) {
bool isPrime = true;
for (int i = 2; i * i <= n; i++) {
if (n % i == 0) {
isPrime = false;
break;
}
}
if (isPrime)
cnt++;
}
cout << cnt << endl;
return 0;
}