#include <iostream>
#include <fstream>
using namespace std;
int n;
bool c[2000000];
int main()
{
  ifstream in("ciur.in");
  in>>n;
  int i,j,nr=0;;
  for(i=2;i*i<=n;i++)
  {
    if(!c[i])
        {
          for(j=i*i;j<=n;j+=i)
            {
              c[j]=true;
              nr++;
            }
        }
  }
  in.close();
  ofstream out("ciur.out");
  out<<nr-1;
  out.close();
  return 0;
}