#include<bits/stdc++.h>
using namespace std;
#define int long long
#define optimize() ios_base::sync_with_stdio(0);cin.tie(0);cout.tie(0);
#define endl '\n'
const int sz = 1e5+5;
const int mod = 1e9+7;

void solve(){
    int n; cin >> n;
    int ans=0;
    if(n==2 || n==3) cout << 1 << endl;
    else{
        int c = n/3;
        if(n%3==0) cout << c << endl;
        else{
            n -= (3*c-1);
            cout << c+(n/2) << endl;
        }
    }

}

signed main(){
    optimize();
    int tc; tc=1;
    while(tc--){
        solve();
    }
}