#include <fstream>

using namespace std;
ifstream in ("ciur.in");
ofstream out ("ciur.out");
int Vector[2000005];

int main()
{
  int N, i, k=2, p=0;
  in>>N;
  Vector[0]=Vector[1]=1;
  for(i=2; i*i<=N; i++)
  {if (Vector[i]==0)
   {for(k=i*i; k<=N; k=k+i)

      {Vector[k]=1;

      }

   }
  }
  for (i=2; i<=N; i=i+1)
  {
      if (Vector[i]==0)
      p=p+1;
  }
out<<p;



    return 0;
}