#include <fstream>
#include <iostream>
using namespace std;
ifstream fin("ciur.in");
ofstream fout("ciur.out");
 char sir[1000001];
 long long int n,i,j,k=1;
int main()
{

   fin>>n;
 for (i = 1; ((i * i) << 1) + (i << 1) <= n; i=i+1)
    {

    if (sir[i] == 0)
    {
      for (j = ((i * i) << 1) + (i << 1); (j << 1) + 1 <= n; j=j+(i << 1) + 1)
        {

        sir[j] = 1;
      }
    }
  }
  for (i=1; 2 * i + 1 <= n; i++)
      if (sir[i] == 0)
        k++;
   fout<<k;

    return 0;
}