#include <fstream>

using namespace std;

const int VMAX = 2e6;

bool c[VMAX+1];

int main()
{
    ifstream in("ciur.in");
    ofstream out("ciur.out");
    int n;
    in >> n;
    for (int i = 2; i * i <= n; i++)
    {
        if (!c[i])
        {
            for (int m = i * i; m <= n; m += i)
            {
                c[m] = true;
            }
        }
    }
    int nr_prime = 0;
    for (int i = 2; i <= n; i++)
    {
        if (!c[i])
        {
            //out << i << " ";
            nr_prime++;
        }
    }
    out << nr_prime << "\n";
    in.close();
    out.close();
    return 0;
}