#include <fstream>

using namespace std;
int n;
bool a[2000010];
int cb( )
 {
  int i, j, nr = 1;
  for (i = 1; ((i * i) << 1) + (i << 1) <= n; i += 1)
    if (a[i] == 0)
      for (j = ((i * i) << 1) + (i << 1); (j << 1) + 1 <= n; j += (i << 1) + 1)
        a[j] = 1;
  for (i=1; 2 * i + 1 <= n; ++i)
      if (a[i] == 0) nr++;
  return nr;
  }
ifstream f("ciur.in");
ofstream g("ciur.out");
int main()
{    f>>n;
      g<<cb();
    return 0;
}