#include <fstream>
#include <math.h>
#include <iostream>
using namespace std;
int M,N,x,i;
bool b;
int main () {
    ifstream in;
    in.open("ciur.in");
    in >> N;
    for (x=2;x<=N;x++) {
        b=true;
        for (i=2; i<=sqrt(x); i++)
          {
              if (x%i==0)
              {
                  b=false;
                  break;
              }
          }
        if (b) { ++M;}
    }
    ofstream out;
    out.open("ciur.out");
    out << M;
    out.close();
}