// Created by PhantomCracker. Copyright (c) PhantomCracker

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

int ciurul_eratostene(int n)
{
	int nr = 0;
	bool v[1000001];
	for(int i=2; i<=n; i++)
		v[i] = 1;
	for(int i=2; i<=sqrt(n); i++)
		if(v[i])
			for(int j=i; j<=n/i; j++)
				v[i*j] = 0;
			for(int i=2; i<=n; i++)
				if(v[i]) nr++;
			return nr;
}

int main()
{
	ifstream f("fractii.in");
	ofstream g("fractii.out");

	int n, numar_fractii;
	int fractii[1000001];

	f>>n;
	g<<ciurul_eratostene(n);
	cout<<endl;
	return 0;
}