#include <fstream>
using namespace std;
ifstream fin("ciur.in");
ofstream fout("ciur.out");
int *p=new int[2000000];
       


int main()
{
  int n, i, j, nr = 0;
  fin>>n;
  for (i = 2; i <= n; ++i) 
{
    if (p[i] == 0) 
    {
      nr++;
      for (j = i + i; j <= n; j += i) 
             {
        p[j] = 1;
             }
    }
}

  fout<<nr;
  
  fin.close();
  fout.close();

  return 0;
    
}