#include <iostream>
#include <fstream>
using namespace std;

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

bool viz[2000001];

int main(){
  int n;
  in>>n;


  int nr = 0;
  for(int i = 2; i <= n; i++){
    if(viz[i] == false){
      nr++;

      for(int j = i; j <= n; j += i){      
          viz[j] = true;
      }

    }
  }
  out<<nr;
  return 0;
}