# include <fstream>
using namespace std;
ifstream cein ("ciur.in"); //("grader_test3.in");
ofstream ceou ("ciur.out");
long long n,k,i,p,m;
bool a[2000000];
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;
  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++;
  return k;
}