#include <iostream>
#include <fstream>
#include <cmath>
using namespace std;
int a[2000001];
int main()
{
  int i, j, n, nr = 0;
  ifstream f("ciur.in");
  ofstream g("ciur.out");
  f >> n;
  for (i = 2; i <= sqrt(n); i++) {
    if (a[i] == 0)
      for (j = i*i; j <= n; j += i)
        a[j] = 1;
    nr++;
  }
  g << nr;
  f.close ();
  g.close ();
  return 0;
}