//
//  main.cpp
//  Problema Ciurul lui Eratosthenes
//
//  Created by Maria Duțu on 02/09/2020.
//  Copyright © 2020 Maria Duțu. All rights reserved.
//

#include <iostream>
#include<fstream>
using namespace std;
int main()
{ ifstream fin ("ciur.in");
    ofstream fout ("ciur.out");
    int N, nr=0, v[2000000], i;
    fin>>N;
    for ( i=2; i<=N; i++)
        v[i]=1;
    for ( i=2; i<= N; i++)
        if (v[i])
        { nr++;
            for(int j=i+i;j<=N; j+=i)
                v[j]=0;
        }
    
    fout << nr;
    fin.close();
    fout.close();
    return 0;
}