#include <iostream>
#include <fstream>
using namespace std;
int a[400001];
int main()
{
  int nr = 0; int i, j, n;
  ifstream f("ciur.in");
  ofstream g("ciur.out");
  f >> n;
  for (i = 2; i <= n; i++) {
    if (a[i] == 0) {
      a[i] = 1;
      for (j = i + i; j <= n; j += i)
        a[j] = 1;
      nr ++;
    }
  }
  g << nr;
  f.close ();
  g.close ();
  return 0;
}