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