#include <cstdlib>
#include <iostream>
#include<fstream>
using namespace std;
ifstream f("ciur.in");
ofstream g("ciur.out");

bool v[2000001];


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