#include <fstream>

using namespace std;

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

const int max_size = 2e6 + 1;

int n, ans;
bool ciur[max_size];

void ciuru ()
{
    ciur[0] = 1;
    ciur[1] = 1;
    for (int i = 2; i <= n; i++)
    {
        if (ciur[i] == 1)
        {
            continue;
        }
        ans++;
        for (int j = 2 * i; j <= n; j += i)
        {
            ciur[j] = 1;
        }
    }
}

int main ()
{
    in >> n;
    ciuru();
    out << ans;
    in.close();
    out.close();
    return 0;
}