//
//  main.cpp
//  ciur
//
//  Created by Catalina Brinza on 10/19/13.
//  Copyright (c) 2013 Catalina Brinza. All rights reserved.
//

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

int main()
{int n,i,nr=0;
    ifstream f("ciur.in");
    ofstream g("ciur.out");
    bool a[2000001];
    f>>n;
    for (i=2;i<=n;i++)
        a[i]=true;

    for (i=2;i<=n;i++)
        if (a[i]==true)
        {
            nr++;
            for (int j=i;j<=n/i;j++) a[i*j]=false;
        }
    g<<nr;
    f.close();
    g.close();
    return 0;
}