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

int main() {
  int n;
  int i, cnt = 0, j;
  bool prim[2000025];
  fin >> n;
  for (i = 2; i <= n; i++) {
    prim[i] = 1;
  }
  for (i = 2; i <= n; i++) {
    if (prim[i]) {
      cnt++;
      for (j = i + i; j <= n; j += i)
        prim[j] = 0;
    }
  }
  fout << cnt;
}