#include <fstream>
#include <vector>

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

    int n;
    fin >> n;

    std::vector<bool> prim(n + 1, true);

    prim[2] = true;
    for (int i = 2; i <= n; i++)
    {
        if (prim[i])
        {
            for (int j = i + i; j <= n; j += i)
            {
                prim[j] = false;
            }
        }
    }

    int count = 0;
    for (int i = 2; i <= n; i++)
    {
        if (prim[i])
        {
            count += 1;
        }
    }

    fout << count << '\n';

    return 0;
}