268B - Buttons - CodeForces Solution

#include "bits/stdc++.h"
using namespace std;
using ll = long long;
const ll N = 1e5 + 7, inf = LLONG_MAX;
#define fastik ios_base::sync_with_stdio(false); cin.tie(nullptr);
#define ff first
#define ss second
#define all(a) a.begin(), a.end()
#define rall(a) a.rbegin(), a.rend()
typedef vector<ll> vec;
typedef vector<vec> vec_;
void solve(){ fastik;
    ll n, m = 0; cin >> n;
    for(ll i = 0; i < n; i++) m += (n - i + ((n - i - 1) * i));
    cout << m;
}
signed main (){ fastik;
    ll test = 1; //cin >> test;
    while(test--) solve(), cout << '\n';
    cin.get();
    return 0;
}
//  - 32 !- 33 "- 34 #- 35 $- 36 %- 37 &- 38 '- 39 (- 40 )- 41 *- 42 +- 43 ,- 44 -- 45 .- 46 /- 47 
// 0- 48 1- 49 2- 50 3- 51 4- 52 5- 53 6- 54 7- 55 8- 56 9- 57 :- 58 ;- 59 <- 60 =- 61 >- 62 ?- 63 
// @- 64 A- 65 B- 66 C- 67 D- 68 E- 69 F- 70 G- 71 H- 72 I- 73 J- 74 K- 75 L- 76 M- 77 N- 78 O- 79 
// P- 80 Q- 81 R- 82 S- 83 T- 84 U- 85 V- 86 W- 87 X- 88 Y- 89 Z- 90 [- 91 \- 92 ]- 93 ^- 94 _- 95 
// `- 96 a- 97 b- 98 c- 99 d-100 e-101 f-102 g-103 h-104 i-105 j-106 k-107 l-108 m-109 n-110 o-111 
// p-112 q-113 r-114 s-115 t-116 u-117 v-118 w-119 x-120 y-121 z-122 {-123 |-124 }-125 ~-126 -127