#include <iostream>
#include <fstream>

using namespace std;

ifstream fin ("ciur.in");
ofstream fout ("ciur.out");

int n, v[2000001];

int main (){

      fin>>n;

      int p=0, x;

      for(int i=2; i<=n; i++){

            if(v[i]==0){
                  p++;

                  x=i;

                  while(i+x<=n){
                        v[i+x]=1;

                        x=x + i;
                  }

            }


      }

      fout<<p;

      return 0;
}