#include <fstream>
using namespace std;

ifstream in ("ciur.in");
ofstream out ("ciur.out");

const int NMAX = 2e6 + 5;

bool NuePrim[NMAX];
int N;

int Ciur (int N) {
    int nr = 0;
    for (int i = 2; i <= N; ++ i) {
        if (NuePrim[i] == false) {
            ++ nr;
            int x = 2;
            while (i * x <= N) {
                NuePrim[i*x] = true;
                ++ x;
            }
        }
    }

    return nr;
}


int main()
{
    in >> N;
    out << Ciur (N);
    return 0;
}