#include <iostream>
#include <fstream>
using namespace std;


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

bool prim[12000002];
int ct;
int main()
{
  int n;
  in>>n;

  for(int i=2;i<=n; ++i)
    prim[i] = 1;
  for(int i = 2;i<=n; ++i)
    if(prim[i])
    {
      ct++;
      for(int j = 2*i; j<=n;j+=i)
        prim[j] = 0;
    }
  out<<ct;
}