\begin{array}{c} \color{#db1616}{\texttt{#Khoadang09}} \end{array}
`@`$\texttt{C++ 1: }$

#include <bits/stdc++.h>
#define buff ios_base::sync_with_stdio(false); cin.tie(NULL); cout.tie(NULL);
#define int long long
using namespace std;
signed main(){
    buff;
    int n; cin >> n;
    int sum_3 = 0;
    for (int i=0;i<=n;i+=3) sum_3 += i;
    cout << sum_3;
    return 0;
}

`@`$\texttt{C++ 2: }$

#include <bits/stdc++.h>
#define buff ios_base::sync_with_stdio(false); cin.tie(NULL); cout.tie(NULL);
#define int long long
using namespace std;
signed main(){
    buff;
    int n; cin >> n;
    int tprr_save = n / 3;
    cout << 3 * tprr_save * (tprr_save + 1) / 2;
    return 0;
}

#include <iostream>
using namespace std;

int main() {
    long long n;
    cin >> n;

    long long div = n / 33;
    long long total = div * (div + 1) / 2 * 33;

    cout << total << endl;

    return 0;
}