#include <iostream>
#include <fstream>

using namespace std;

int prim(int a)
{
  int k=0;
  long long i;

  for (i=2;i*i<=a;++i)
    if (a%i==0)
      return 0;
  if (a==1 || a==0)
    return  0;

 return 1;

}

int main()
{
  int n,i,k=0;

  ifstream f("ciur.in");
  ofstream g("ciur.out");

  f>>n;

  for (i=1;i<=n;++i)
    if (prim(i)==1)
      k++;
  g<<k;

  return 0;
}