#include<fstream>
#include<iostream>
using namespace std;
ifstream f("ciur.in");
ofstream g("ciur.out");
int nr=1,n,i,j,v[2000002];
int main()
  {
     f>>n;
     if (n<2)
         {g<<0;
         return 0;}
     for (i=3;i<=n;i=i+2)
           if (v[i]==0)
             {nr++;
              for (j=i+i;j<=n;j=j+i)
                 v[j]=1; }
    g<<nr;
    return 0;
  }