#include <iostream>
#include <fstream>
#define nmax 2000001
using namespace std;

ifstream fin("ciur.in");
ofstream fout("ciur.out");

int c[nmax];

int main()
{   int n,i,j,ct=0;
    fin>>n;
    c[2]=true;
    for(i=3;i<=n;i+=2) c[i]=true;
    for(i=3;i*i<=n;i++)
        if(c[i]==true)
            for(j=3*i;j<=n;j=j+2*i)
                c[j]=false;
    for(i=2;i<=n;i++)
        if(c[i]==true) ct++;
    fout<<ct<<'\n';


    return 0;
}