#include<iostream>
#include<fstream>
using namespace std;
ifstream fin("ciur.in");
ofstream fout("ciur.out");
int main ()
{
    int n;
    fin>>n;
    bool a[n];
    for (int i=2;i<=n;i++)
    {
        a[i]=0;
    }
    int ct=0;
    for (int i=2;i<=n;i++)
    {
        if (a[i]==0)
        {
            ct++;
            for (int j=i+i;j<=n;j=j+i)
            {
                a[j]=1;
            }
        }
    }
    fout<<ct;
}