#include <iostream>
#include<fstream>
using namespace std;
ifstream fin("euclid2.in");
ofstream fout("euclid2.out");
bool c[2000001];
int main()
{   int n,i,ct,j;
    fin>>n;
    fin.close();
    c[2]=true;
    for(i=3;i<=n;i=i+2)c[i]=true;
    for(i=3;i*i<=n;i=i+2)
       if(c[i]==true)
          for(j=3*i;j<=n;j=j+2*i)c[j]=false;
    ct=0;
    for(i=1;i<=n;i++)if(c[i]==true)ct++;
    fout<<ct;


    fout<<"\n";
    fout.close();



    return 0;
}