#include <iostream>
#include <fstream>
#include <string>
using namespace std;

long long n , cont;
bool x[2000005];

int main ()
{
	ifstream f ("ciur.in");
	ofstream g ("ciur.out");
	
	f >> n;
	
	x[1] = 1;
	
	for (int i = 2 ; i <= n ; ++i)
		if (!x[i])
			for (int j = i + i ; j <= n ; j += i)
				x[j] = 1;
	
	for (int i = 1 ; i <= n ; ++i)
		if (!x[i])
			cont++;
	
	g << cont;
	
	return 0;
}