#include <fstream>
#include <bitset>

using namespace std;

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

const int max_size = 2e6 + 1;

bitset <max_size> pr;
int ans;

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

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