#include <iostream>
#include <cstdio>

using namespace std;

int main() {

  freopen("ciur.in", "r", stdin);
  freopen("ciur.out", "w", stdout);
   int count = 1, N;


  scanf("%d", &N);
   for(int  i=3; i<=N; i+=2)
   {
    bool prim = true;
       for(int j = 2; (j*j < N && j < i); ++j)
       {
           if(i%j == 0)
           {
           prim = false;
            break;
           }
       }

       if(prim == true)
       count++;
   }

   printf("%d\n", count);


    return 0;
}