#include <iostream> #include <vector> #include <cmath> bool is_prime(int num) { if (num <= 1) { return false; } if (num == 2 || num == 3) { return true; } if (num % 2 == 0) { return false; } int sqrt_num = static_cast<int>(sqrt(num)); for (int i = 3;i <= sqrt_num;i += 2) { if (num % i == 0) { return false; } } return true; } int count_primes(int n) { int count = 0; for (int i = 2;i <= n;i++) { if (is_prime(i)) { count++; } } return count; } int main() { int n; std cin >> n; std cout << count_primes(n) << std endl; return 0; }