# include <fstream>
using namespace std;
ifstream cein ("ciur.in");
ofstream ceou ("ciur.out");
int n,k,i,y,x,m;
bool a[1001];
int ciur ();
void ceifs ()
{
  cein>>n;
}
void ceofs ()
{
  ceou<<ciur();
}
int main ()
{
  ceifs ();
  k = 0;
  ceofs ();
}
int ciur ()
{
  for (i = 2; i <= n; i++)
    a[i] = true;
    if (a[i])
  for (y = 2; y <= n; y++)
      for (m = 2*y; m <= n; m += y)
        a[m] = false;
  for (x = 2; x <= n; x++)
    if (a[x])
      k++;
  return k;
}