Loops

#include <iostream>

using namespace std;

long long solve(int n) {
    long long x = 0;
    for (int a = 1; a <= n; a++)
      x += (n-a+1)*(1-a) + (n-a+1)*(a+n)/2;
      // x += n+1+(n+1)*n/2 - a*(1+n+1+n/2-(n+1)/2) + a**2*(1-1/2)
    return x;
}

int main() {
    long long n;
    cin >> n;
    cout << solve(n) << endl;
}

Test 1

Verdict: ACCEPTED

Test 2

Verdict: ACCEPTED

Test 3

Verdict: ACCEPTED

Test 4

Verdict: ACCEPTED

Test 5

Verdict: ACCEPTED

Test 6

Verdict: WRONG ANSWER

Test 7

Verdict: WRONG ANSWER

Test 8

Verdict: WRONG ANSWER

Test 9

Verdict: WRONG ANSWER

Test 10

Verdict: WRONG ANSWER

Test 11

Verdict: WRONG ANSWER

Test 12

Verdict: WRONG ANSWER

Test 13

Verdict: WRONG ANSWER

Test 14

Verdict: WRONG ANSWER

Test 15

Verdict: WRONG ANSWER

Test 16

Verdict: WRONG ANSWER

Test 17

Verdict: WRONG ANSWER

Test 18

Verdict: WRONG ANSWER

Test 19

Verdict: WRONG ANSWER

Test 20

Verdict: WRONG ANSWER