#include<iostream>
#include<fstream>

using namespace std;

ifstream f("ciur.in");
ofstream g("ciur.out");

int main ()
{
    int n,ct;
    f>>n;
    ct=0;
    bool prim[n];
    for (int i=2;i<=n;i++)
    {
        prim[i]=1;
    }
    for (int i=2;i<=n;i++)
    {
        if (prim[i]==1)
        {
            ct++;
            int j;
            for (j=i+i;j<=n;j=j+i)
            {
                prim[j]=0;
            }
        }
    }
    g<<ct;
}