//Infoarena. Arhiva Educationala. Ciurul lui Eratostene.
#include<iostream>
#include<fstream>
using namespace std;

bool ciur[2000005],n;

int main(){
    freopen("ciur.in","r",stdin);
    freopen("ciur.out","w",stdout);
    cin>>n;

    int ct=0;

    for(int i=2;i<=n;i++){
        if(ciur[i]==0){
            ct++;
            for(int j=i+i;j<=n;j+=i) ciur[j]=1;
        }
    }

    cout<<ct;

}