#include <fstream>
using namespace std;
ifstream in ("ciur.in");
ofstream out ("ciur.out");
bool v[2000001];
int main ()
{
    int n,i,j, cont=0;
    in>>n;

    for (i=2;i<=n;i++)

    {
        if (v[i] == 0)
            cont++;
            {
                for(j=i+i;j <= n;j=j+i)
                    v[j] = 1;
            }
    }
    out<<cont;
}