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

#include <iostream>
#include <fstream>

using namespace std;

char a[2000000];

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

int main(int argc, const char * argv[])
{
    ifstream f("ciur.in");
    ofstream g("ciur.out");
    int N;
    cin>>N;
    cout<<Eratosthenes(N);
    return 0;
}