#include <fstream>

using namespace std ;

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

const int MAX = 2e6 + 14 ;

bool isNotPrime [MAX] ;

int main() 
{
	int n ;
	cin >> n ;
	int Sol = 0 ;
	for (int i = 2 ; i <= n ; ++ i) {
		if (isNotPrime [i] == 0) {
			for (int j = i+i ; j <= n ; j += i) {
				isNotPrime [j] = 1 ;
			}
			++ Sol ;
			//cout << i << '\n' ;
		}
	}
	cout << Sol << '\n' ;
	return 0 ; 
}