#include <iostream> using namespace std; bool isPrime(int num) { if (num <= 1) return false; if (num <= 3) return true; if (num % 2 == 0 || num % 3 == 0) return false; for (int i = 5; i * i <= num; i += 6) { if (num % i == 0 || num % (i + 2) == 0) return false; } return true; } int main() { int n; cin >> n; int count = 0; for (int i = 2; i <= n; ++i) { if (isPrime(i)) ++count; } cout << count << endl; return 0; }