#include <iostream>
#include <fstream>
using namespace std;
int main () {
     int n,k=0;
     ifstream fd("ciur.in");
     ofstream df("ciur.out");
     fd>>n;
     bool a[n+1];
     for (int i=2;i<=n-1;i++){
         a[i]=true;
         }
     for (int j=2;j<=n-1;j++){
         if (a[j]){
                   k=k+1;
                  for (int i=j;i<=n-1;i=i+j){
                      a[i]=false;
                    
                      }
             
               }
         }
         df <<k<<" ";
    fd.close();
    df.close();
         return (0);
     }