#include <fstream>
using namespace std;

const int kXMax = 2000010;
int x, sol;
bool viz[kXMax];

void Citire() {
    ifstream in("ciur.in");
    in >> x;
    in.close();
}

void Solve() {
    if(x >= 2)
        sol = 1;
    for (int i = 3; i <= x; i += 2)
        if(!viz[i]) {
            sol++;
            for (int j = i; j <= x; j += i)
                viz[j] = 1;
        }
}

void Afisare() {
    ofstream out("ciur.out");
    out << sol << '\n';
    out.close();
}

int main() {
    Citire();
    Solve();
    Afisare();
}