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

bool a[2000006];
int n, k;

void Ciur()
{
   int i, j;
   for (i=3; i*i<=2000003; i=i+2)
   {
      for (j=i*i; j<=2000003; j=j+i)
         a[j] = 1; /// compus
   }
}

void Numara()
{
   int i;
   fin >> n;
   k=1;
   for (i=3; i<=n; i=i+2)
     if (!a[i])
      k++;  
   fout << k;
}


int main ()
{
  Ciur();
  Numara();
  fout << "\n";
  return 0;
}