#include <iostream>
#include <fstream>
using namespace std;

int main()
{
   unsigned N,d,i,k=0,nr_prim=0;
   ifstream f("ciur.in");
   ofstream g("ciur.out");
   f>>N;
   for(i=2;i<=N;i++)
   {k=0;
       for(d=2;d<=i/2;d++)


           if(i%d==0)
            k=k+1;

       if(k==0)
        nr_prim=nr_prim +1;

   }
   g<<nr_prim;
   f.close();
   g.close();
    return 0;
}