#include <fstream>
using namespace std;
ifstream fin("ciur.in");
ofstream fout("ciur.out");

int getTheNumber(int n) 
{
int *p=new int[2000000];
       
  int i, j, nr = 0;
  for (i = 2; i <= n; ++i) 
{
    if (p[i] == 0) 
    {
      nr++;
      for (j = i + i; j <= n; j += i) 
             {
        p[j] = 1;
             }
    }
}
  return nr;
  
  
}

int main()
{
  int n;

  fin>>n;
  fout<<getTheNumber(n);
  fin.close();
  fout.close();

  return 0;
    
}