#include <fstream>

using namespace std;

ifstream f("ciur.in");
ofstream g("ciur.out");

int v[2000001],x,nr,k,n;
int main()
{  f>>n;
   nr=0;
   for(x=2;x<=n;x++)
      if(v[x]==0){ nr++;
                   k=2;
                   while(k*x<=n){v[k*x]=1;
                                 k++;
                                }
                 }
  g<<nr<<'\n';
  f.close();g.close();
  return 0;
}