#include <fstream>
#include <math.h>
using namespace std;
const int N_MAX = 2000000;
bool compus[N_MAX + 1];
int gasite;
ifstream ka("ciur.in");
ofstream ki("ciur.out");

int main()
{
   int n;
   ka >> n;
   for(int i = 2; i <= n; i++)
   {
      if(!compus[i])
      {
	 gasite++;
         for(int d = i * i; d <= n; d += i)
            compus[d] = true;
      } 
   }
   ki << gasite;
}