#include <fstream>
using namespace std;

int v[2000000]; //0 nemarcat, 1 marcat

int main(){
  int n;
  ifstream fin("ciur.in");
  ofstream fout("ciur.out");
  fin>>n;
  int cate=0;


  for(int start=2; start<=n; start++)
  {
    if(v[start]==1)
      continue;
    cate++;
    for(int contor=start; contor<=n; contor+=start)
      v[contor]=1;
  }
  fout<<cate;

  return 0;
}