#include <fstream>
using namespace std;
ifstream f ("ciur.in");
ofstream g ("ciur.out");
int n,nrp;
bool B [2000001];
int main ()
{
    f >> n;
    if (n >= 2)
    {
        nrp = 1;
        for (int i = 2; i <= n; i = i +2)
            B [i] = 1;
        for (int i = 3; i <=n; i = i + 2)
            if (B [i] == 0)
            {
                nrp = nrp + 1;
                for (int j = i + i; j <= n; j = j +i)
                     B [j] = 1;
            }
    }
    g << nrp;
    g.close ();
    return 0;
}