/*
 */

#include <fstream>
#include <iostream>
using namespace std;
ifstream f("ciur.in");
ofstream g("ciur.out");

int N, i, cnt;
bool prim[2000025];
int main() {
  f >> N;
  for (i = 2; i <= N; ++i)
    prim[i] = 1;

  for (i = 2; i <= N; ++i) {
    if (prim[i]) {
      ++cnt;
      for (int j = i + i; j <= N; j = j + i) {
        prim[j] = 0;
      }
    }
  }

  g << cnt;

  return 0;
}

// https://infoarena.ro/problema/ciur (
// https://ro.wikipedia.org/wiki/Ciurul_lui_Eratostene )
// https://infoarena.ro/problema/sdo
// https://www.infoarena.ro/problema/alibaba
// https://infoarena.ro/problema/cautbin
// https://www.pbinfo.ro/probleme/277/varfuri