#include <iostream>
#include <fstream>

using namespace std ;

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

bool v[2000005] ;

int main()

{
    register int n , i , j , x , nr = 0 ;
	v[0] = v[1] = 1 ;
	for( i = 3 ; i * i <= 2000000 ; i = i + 2 )
       if ( v[i] == 0 )
        for( j = 3 ; i * j <= 2000000 ; j = j + 2 )
				  v[i*j] = 1 ;
	f >> n ;
    if ( n >= 2 )
        ++nr ;
	for( i = 3 ; i <= n ; ++i )
        if ( i % 2 == 1 && v[i] == 0 ) ++nr ;

	g << nr ;
	return 0 ;
}