#include<iostream>
#include<fstream>
using namespace std;
int main ()
{
    ifstream fin("ciur.in");
    ofstream fout("ciur.out");
    int N,ct;
    fin>>N;
    ct=0;
    int 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;
            }
        }
    }
    fout<<ct;
}