#include <iostream>
#include <cstdio>
#include <cstdlib>

using namespace std ;

const int MAXN = 2000000 ;

bool binar [ MAXN ] ;

int n , k ;

int main ( )
{
  freopen ( "ciur.in" , "r" , stdin ) ;
  freopen ( "ciur.out" , "w" , stdout ) ;
  cin >> n ;
  int i , j  ;
  for ( i = 2 ; i <= n ; ++i )
  {
    if ( !binar [ i ] )
    {
      for ( j = i << 1 ; j <= n ; j += i )
	binar [ j ] = true ;
      ++ k ;
    }
  }
  cout << k << endl ;
  
  return 0 ;
}