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

#include <iostream>
#include <fstream>
#define N_MAX 3000000
using namespace std;
class Eratosthenes{
    int n;
    char a[N_MAX];
    int count;
public:
    Eratosthenes(int n);
    int getNumberOfPrimes();
    int* getPrimes(int arr[]);
};

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

int Eratosthenes::getNumberOfPrimes(){
    return count;
}

int* Eratosthenes::getPrimes(int arr[]){
    int i,j=0;
    for(i=2;i<=n;i++)
        if(a[i]==0){
            arr[j++]=i;
        }
    return arr;
}

int main(int argc, const char * argv[])
{
    int n;
    ifstream f("ciur.in");
    ofstream g("ciur.out");
    cin>>n;
    Eratosthenes interval(n);
    cout<<interval.getNumberOfPrimes();
    //cout<<'\n';
    
    /*int array[20000];
    int *vector=interval.getPrimes(array);
    
    int i=0;
    while(vector[i]){
        cout<<vector[i]<<" ";
        i++;
    }*/
    return 0;
}