/* 
*   @author:- SYEDA SADIATUL JANNAT TUSHI
*   date & time :2024-10-03 20:44:55
*   BANGLADESH , SYLHET. 
*/

#include <bits/stdc++.h>
using namespace std;

#define endl '\n'
#define rep(i, a, b) for(int i = (a); i < (b); i++)
#define ll long long
#define sz(x) (int)x.size()
#define vi vector<ll>
#define fast ios_base::sync_with_stdio(false);cin.tie(0);cout.tie(0);

void solve(){
    ll n; cin>>n;

    if(n%3==0){
        cout<<n/3<<endl;
    }
    else if(n%3==1){
        ll a=n/3-1;
        ll b=n-(3*a);
        ll ans=b/2;
        cout<< a+ans<<endl;
    }
    else if(n%3==2){
        cout<<n/3+1<<endl;
    }
}
 
int main() {
    fast
    ll t=1;//cin>>t;
    while (t--) {
        solve();
    }
    return 0;
}