#include <iostream>
#include <fstream>

using namespace std;

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

bool nuEPrim[2000001];
int n, nrElemPrime;

int ciur(){
  for(int i = 2; i <= n; i++){
    if(nuEPrim[i] == false){
      nrElemPrime ++;
      for(int j = i ; j <= n; j+= i)
        if(j % i == 0)
          nuEPrim[j] = true;
    }
  }
  return nrElemPrime;
}

int main(){
  in >> n;
  out << ciur();
  return 0;
}