#include<bits/stdc++.h>
using namespace std;
#define endl '\n'
#define ll long long int
#define vv vector<long long>
#define mpp map<long long,long long>
#define ms multiset<long long>
#define ss set<long long>
#define vp vector<pair<long long, long long>>
#define MOD 1000000007
#define YES cout<<"YES"<<endl
#define NO cout<<"NO"<<endl
#define all_v v.begin(),v.end()
#define all_a a.begin(),a.end()
#define sort_rev sort(v.rbegin(),v.rend());
#define all_n for(int i=0;i<n;i++)
#define print for(auto it:v)cout<<it<<" "
#define print_vp for(auto it:vp)cout<<it.first<<" "<<it.second<<endl
#define print_mp for(auto it:mp) cout<<it.first<<" "<<it.second<<endl
void requisite(){
    ios::sync_with_stdio(false);
    cin.tie(nullptr);cout.tie(nullptr);
}
int main() {
    requisite();
    ll n;
    cin>>n;
    ll count=0;
    count+=n/3;
    n=n%3;
    if(n==1){
        count--;
        n=4;
    }
    else if (n==2) n=2;
    else n=0;
    count+=n/2;
    cout<<count<<endl;

    return 0;
}