//
//  main.cpp
//  Ciurul lui Eratosthenes
//
//  Created by Alex Petrache on 09/07/14.
//  Copyright (c) 2014 Alex Petrache. All rights reserved.
//

#include <fstream>

using namespace std;

int a[2000000];

void Eratosthenes(){
    int i,j;
    for(i=2;i<=2000000;i++){
        if(a[i]==0){
            for(j=i+i;j<=2000000;j+=i)
                a[j]=1;
        }
    }
}

int main(int argc, const char * argv[])
{
    ifstream f("ciur.in");
    ofstream g("ciur.out");
    int N;
    f>>N;
    Eratosthenes();
    int count=0;
    for(int i=2;i<=N;i++)
        if(!a[i])
            count++;
    g<<count;
    return 0;
}