#include <fstream> 

using namespace std ;

const int MAX = 2e6 + 14 ;

bool prime [MAX] ; 

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

int main () 
{
	int n ; 
	cin >> n ; 
	int sol = 0 ; 
	for ( int i = 2 ; i <= n ; ++ i ) {
		if ( prime [i] == 0 ) {
			for ( int j = i + i ; j <= n ; j += i ) {
				prime [j] = 1 ; 
			}
			++ sol ; 
		}
	}
	cout << sol ;
	return 0 ; 
}