#include <fstream>

using namespace std;

const int MAX = 2000020;

int N;
bool taken[MAX];

int Ciur(int N) {
    int Ans = 0;
    for(int i = 2; i <= N; i++) {
        if(!taken[i]) {
            Ans++;
            for(int j = 2 * i; j <= N; j += i)
                taken[i] = true;
        }
    } return Ans;
}

int main() {
    ifstream in("ciur.in");
    in >> N;
    in.close();

    ofstream out("ciur.out");
    out << Ciur(N) << "\n";
    out.close();
}