#include <fstream>

void szita(int x, bool *t)
{
    for (int i = 2; i * i <= x; i++)
    {
        if (!t[i])
        {
            for (int j = i * i; j <= x; j += i)
            {
                t[j] = true;
            }
        }
    }
}

int main()
{
    std::ifstream in("ciur.in");
    int x;
    in >> x;
    in.close();

    bool *t = new bool[x + 1]();
    t[0] = t[1] = true;
    szita(x, t);

    int db = 0;
    for (int i = 2; i <= x; i++)
    {
        if (!t[i])
        {
            db++;
        }
    }

    std::ofstream out("ciur.out");
    out << db;

    out.close();
    delete[] t;
    return 0;
}