#include <iostream>
#include <fstream>
#define N 2000001

using namespace std;

ifstream fin ("ciur.in");
ofstream fout ("ciur.out");

int main ()
{

  int c;
  int cont=0;
  fin >> c;
  for (int i=2; i<=c; i++)
  {
    if (v[i]==0)
    {
      for (int j=i+i; j<=c; j=j+i)
          v[j]=1;
      cont++;
    }
  }
  fout << cont;


}