#include <fstream>
#include <vector>
using namespace std;

vector<int> filterPrimes(int n){
    vector <int> primes;
    vector <bool> isPrime(n, true);

    for (int i = 2; i <= n; ++i){
        if (isPrime[i]){
            primes.push_back(i);
            for (int j=2; j * i <= n; ++j){
                isPrime[i * j] = false;
            }
        }
    }
    return primes;
}

int main(){
    ifstream cin("ciur.in");
    ofstream cout("ciur.out");
    int n;

    cin >> n;
    vector <int> primes = filterPrimes(n);
    cout << primes.size() << "\n";
    cin.close();
    cout.close();
    return 0;
}