#include<iostream>
#include<cstdio>
#include<cmath>
using namespace std;

int main(){
  int n,prime[1000001],key,lf=0;
  prime[0]=2;
  key=1;
  for(int i=3;i<=999999;i+=2)
    {
      for(int j=2;j<=sqrt(i);j++)
	{
	  if(i%j == 0)
	    {
	      lf=1;
	      break;
	    }
	}
      if(lf == 1)
	{
	  lf=0;
	}
      else 
	{
	  prime[key]=i;
	  key++;
	}
    }

  while(cin >> n)
{
  int cou=0;
  for(int i=0;;i++)
    {
      if(prime[i] <= n)
	{
	  cou++;
	}
      else break;
    }

  cout << cou << endl;
 }
}