Problem p02624 (C++) — buggy submission, verdict: Time Limit Exceeded

/*==============================================*\\
Codeforces ID:    mdshihab
 Atcoder ID :   mdshihab                                                 |
Name:     Md. Shihabul Minhaz                     |
Study:      CSE, JKKNIU                           |
Address:  Trishal, Mymensingh, Bangladesh         |
                                                  |
 mail:   mdshihabul20171@gmail.com                |
 FB  :   fb.com/mdshihabul.minhaz.7               |
 github: Shihabulminhaz                           |
stopstalk :  mdshihab                             |
                                                  |
@uthor   Md. Shihabul Minhaz (shihab)             |
\\*===============================================*/

#include <bits/stdc++.h>
using namespace std;
#define fi(a) scanf("%d", &a);
#define fli(a) scanf("%ld", &a);
#define fll(a) scanf("%lld", &a);
#define pi(a) printf("%d\\n", a);
#define ppi(i, a) printf("Case %d: %d\\n", i, a);
#define ll long long
#define fast                                                                   \\
  ios_base::sync_with_stdio(false);                                            \\
  cin.tie(NULL);                                                               \\
  cout.tie(NULL);
void FI() {
#ifndef ONLINE_JUDGE
  freopen("C:\\\\Users\\\\SHIHAB\\\\Desktop\\\\input.in", "r", stdin);
#endif // ONLINE_JUDGE
}
// ll arr[10000000];
int main() {
  fast
      // FI(); /// skip this line for compile
      /// brute force solution
      /*
      ll n,l,j=0,ans=1;
      ll sum=0;
      cin >> n;

      for(ll i=1;i<=n;i++){
          for(ll j=i;j<=n;j+=i){
              arr[j]++;
          }
      }

      for(ll i=1;i<=n;i++){
          sum+=i*arr[i];
      }
      cout << sum << endl;*/

      /// optimize solution
      /* ll cnt,ans=0,sum,n;
       cin >> n;
       for(ll i=1;i<=n;i++){
           cnt = n/i;
           sum = (cnt+1) * cnt/2;
           ans+=sum*i;
       }
       cout << ans << endl;*/

      /// more optimize solution
      ll n,
      ans = 0;
  cin >> n;
  for (ll i = 1; i <= n; i++) {
    for (ll j = i; j <= n; j += i) {
      ans += j;
    }
  }
  cout << ans << endl;
  return 0;
}


Error: TLE

Fixed submission:

/*==============================================*\\
Codeforces ID:    mdshihab
 Atcoder ID :   mdshihab                                                 |
Name:     Md. Shihabul Minhaz                     |
Study:      CSE, JKKNIU                           |
Address:  Trishal, Mymensingh, Bangladesh         |
                                                  |
 mail:   mdshihabul20171@gmail.com                |
 FB  :   fb.com/mdshihabul.minhaz.7               |
 github: Shihabulminhaz                           |
stopstalk :  mdshihab                             |
                                                  |
@uthor   Md. Shihabul Minhaz (shihab)             |
\\*===============================================*/

#include <bits/stdc++.h>
using namespace std;
#define fi(a) scanf("%d", &a);
#define fli(a) scanf("%ld", &a);
#define fll(a) scanf("%lld", &a);
#define pi(a) printf("%d\\n", a);
#define ppi(i, a) printf("Case %d: %d\\n", i, a);
#define ll long long
#define fast                                                                   \\
  ios_base::sync_with_stdio(false);                                            \\
  cin.tie(NULL);                                                               \\
  cout.tie(NULL);
void FI() {
#ifndef ONLINE_JUDGE
  freopen("C:\\\\Users\\\\SHIHAB\\\\Desktop\\\\input.in", "r", stdin);
#endif // ONLINE_JUDGE
}
// ll arr[10000000];
int main() {
  fast
      // FI(); /// skip this line for compile
      /// brute force solution
      /*
      ll n,l,j=0,ans=1;
      ll sum=0;
      cin >> n;

      for(ll i=1;i<=n;i++){
          for(ll j=i;j<=n;j+=i){
              arr[j]++;
          }
      }

      for(ll i=1;i<=n;i++){
          sum+=i*arr[i];
      }
      cout << sum << endl;*/

      /// optimize solution
      /* ll cnt,ans=0,sum,n;
       cin >> n;
       for(ll i=1;i<=n;i++){
           cnt = n/i;
           sum = (cnt+1) * cnt/2;
           ans+=sum*i;
       }
       cout << ans << endl;*/

      /// more optimize solution
      ll n,
      ans = 0;
  cin >> n;
  for (ll i = 1; i <= n; i++) {
    for (ll j = 1; j <= n; j++) {
      if (!(i % j))
        ans += i;
    }
  }
  cout << ans << endl;
  return 0;
}