#include<fstream>
#include<iostream>
#include<vector>

using namespace std;
const int MAX = 2000002;
vector<bool> V(MAX,true);
int N , K;

void ciur(){
    for(int i = 2; i < N; ++i)
       if (V[i]){
                V[i] = false;
                ++K;
          for (int j = 2; j * i < N; ++j)
            V[i * j] = false;
    }
}

int main(){
   ifstream fin("ciur.in");
   ofstream fout("ciur.out");
   fin >> N;
   ciur();
   fout << K;
   fin.close();
   fout.close();
   return 0;
}