#include using namespace std;

bool is_prime(int num) { if (num <= 1) return false; if (num == 2) return true; if (num % 2 == 0) return false; for (int i = 3; i * i <= num; i += 2) { if (num % i == 0) return false; } return true; }

int main() { int n, count = 0; cin >> n; for (int i = 2; i <= n - 2; ++i) { if (is_prime(i) && is_prime(i + 2)) { ++count; } } cout << count << endl; return 0; }