#include<bits/stdc++.h>
#define ll long long int
#define vec vector<ll>
#define mat vector<vector<ll>>

using namespace std;

const ll mod=1000000007;
const ll inf=LONG_LONG_MAX;
ll dx4[4]={1,0,-1,0};
ll dy4[4]={0,-1,0,1};
ll dx8[8]={1,0,-1,1,-1,1,0,-1};
ll dy8[8]={1,1,1,0,0,-1,-1,-1};

int main(){

  ll n;
  cin >> n;
  ll a=0;
  while(3*a<=n){
    a++;
  }
  cout << a-1 << endl;

}
#include<iostream>
using namespace std;
int main(){
  int a;
  cin>>a;
  
  cout<<a/3;
  
  
  return 0;
}
