#include <fstream>
#include <iostream>

using namespace std;

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

bool v[2000000];

int main(){
  int n, contor = 0, j;
  in >> n;
  for(int i = 2; i <= n; ++i){
    if(!v[i]){
      contor++;
      j = 2;
      while(i * j <= n){
	v[i * j] = 1;
	j++;
      }
    }
  }
  out << contor << "\n";
  return 0;
}