#include #include using namespace std;

// 判断是否为素数 bool isPrime(int num) { if (num < 2) return false; if (num == 2) return true; if (num % 2 == 0) return false; int limit = sqrt(num); for (int i = 3; i <= limit; i += 2) { if (num % i == 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;

}