# include <fstream>
using namespace std;
ifstream cein ("ciur.in");//("grader_test10-1.in");
ofstream ceou ("ciur.out");
long long n,k,i,p,m;
bool a[2000001];
void ciur ();
/*void ceifs ()
{
  cein>>n;
  k = 0;
}
void ceofs ()
{
  ceou<<ciur();
}*/
int main ()
{
  /*ceifs ();
  ceofs ();*/
  ciur ();
}
void ciur ()
{
  cein>>n;
  k = 0;
  for (i = 2; i <= n; i++)
    a[i] = true;
  for (p = 2; p <= n; p++)
    if (a[p])
      for (m = 2*p; m <= n; m += p)
        a[m] = false;
  for (i = 2; i <= n; i++)
    if (a[i])
      k++;
  ceou<<k;
}