#include <fstream>
#include <vector>

int main()
{
    std::ifstream fin("ciur.in");
    std::ofstream fout("ciur.out");

    int n;
    fin >> n;

    int cnt = 1, stop = (n - 3) / 2;
    std::vector<bool> is_prim(stop + 1, true);

    if (n > 2)
    {
        for (int i = 0; i <= stop; ++i)
            if (is_prim[i])
            {
                cnt++;
                for (int j = i + 2 * i + 3; j <= stop; j += 2 * i + 3)
                    is_prim[j] = false;
            }
    }

    fout << cnt << std::endl;

    return 0;
}