#include<iostream>
#include<vector>
#include<cmath>
#include<algorithm>
using namespace std;
#pragma GCC target("avx2")
#pragma GCC optimize("O3")
#pragma GCC optimize("unroll-loops")
//#pragma GCC target("sse,sse2,sse3,ssse3,sse4,popcnt,abm,mmx,avx,tune=native")


vector<long long> gen_primes(int N){   //N以下の素数をprimesに入れていく
  vector<bool> isprime(N+1,1); 
  vector<long long> primes;
  isprime[0]=0;
  isprime[1]=0;  

  for (int i=2;i<=N;++i){
    if (isprime[i]){
      primes.emplace_back(i);
      for (int q=i*2;q<=N;q+=i){  
        isprime[q]=0;
      }
    }
  }  
  return primes;   
}

int main(){
  long long N;
  cin >> N;
  auto p=gen_primes(N);
  int m=p.size();  
  int ans=0;
  for (int i=0;i<m;++i){
    
        if (binary_search(p.begin(),p.end(),sqrt(p[i]+2))){
          if (p[i]==2) ++ans;
          else ans+=2;
        	
          
        }  
        
          
    
  }
  cout << ans <<"\n";
}