Problem p04047 (C++)

Buggy submission (status: Runtime Error):
/*
...........__________ ___  __
.............|       | |   /
.............|       | |  /
.............|       |                               | __                | /
_______
.............|_______|  _______            _______   |______   ________   /|  /
|               |/       |      |
.............| \               | |      | |          |      |          | / | /
|               |\       |
.............|  \       _______| |      | |_______   |      |   _______|   |/ |
| \      |
.............|   \      |      | |      |         |  |      |  |       |   | |
|  \     |
...........__|    \__|  |______| |______| ________|  |      |_ |_______|   |
|__|           _|   \__ _|        .

*/
#include <bits/stdc++.h>
using namespace std;
#define int long long
#define ull unsigned long long int
#define ld long double
#define vi vector<int>
#define vii vector<pair<int, int>>
#define vvi vector<vector<int>>
#define pii pair<int, int>
#define prec(x) fixed << setprecision(15) << x
#define all(x) x.begin(), x.end()
#define rall(x) x.rbegin(), x.rend()
#define rev(x) reverse(x.begin(), x.end())
#define mset(a, b) memset(a, b, sizeof(a))
#define mcpy(a, b) memcpy(a, b, sizeof(a))
#define fo0(i, n) for (int i = 0, i##end = n; i < i##end; i++)
#define fo1(i, n) for (int i = 1, i##end = n; i <= i##end; i++)
#define fo(i, a, b) for (int i = a, i##end = b; i <= i##end; i++)
#define foe(i, x) for (__typeof((x).end()) i = (x).begin(); i != (x).end(); ++i)
#define fre(i, x)                                                              \
  for (__typeof((x).rend()) i = (x).rbegin(); i != (x).rend(); ++i)
#define fast                                                                   \
  ios_base::sync_with_stdio(false);                                            \
  cin.tie(0);                                                                  \
  cout.tie(0)
int gcd(int a, int b) { return b ? gcd(b, a % b) : a; }
const int inf = 1e18;
const int mod = 1e9 + 7;
const int N = 2e5 + 9;
void read_And_write() {
#ifndef ONLINE_JUDGE
  freopen("input.txt", "r", stdin);
  freopen("output.txt", "w", stdout);
#endif
}

void raushan_kumar() {
  int d = 0, e = 0, f = 0, g = 0, p = 0, w = 0, flag = 0, ans = 0, res = 0,
      cnt = 0, sum = 0;
  double f1 = 0.0, f2 = 0.0, f3 = 0.0;
  int n;
  cin >> n;
  n *= 2;
  int a[n];
  fo0(i, n) cin >> a[i];
  sort(a, a + n);

  for (int i = 0; i < n; i += 2)
    sum += a[i];
  cout << sum;
}

int32_t main() {
  read_And_write();
  fast;
  int t = 1;
  // cin>>t;
  while (t--) {
    raushan_kumar();
  }
}

Fixed submission:
/*
...........__________ ___  __
.............|       | |   /
.............|       | |  /
.............|       |                               | __                | /
_______
.............|_______|  _______            _______   |______   ________   /|  /
|               |/       |      |
.............| \               | |      | |          |      |          | / | /
|               |\       |
.............|  \       _______| |      | |_______   |      |   _______|   |/ |
| \      |
.............|   \      |      | |      |         |  |      |  |       |   | |
|  \     |
...........__|    \__|  |______| |______| ________|  |      |_ |_______|   |
|__|           _|   \__ _|        .

*/
#include <bits/stdc++.h>
using namespace std;
#define int long long
#define ull unsigned long long int
#define ld long double
#define vi vector<int>
#define vii vector<pair<int, int>>
#define vvi vector<vector<int>>
#define pii pair<int, int>
#define prec(x) fixed << setprecision(15) << x
#define all(x) x.begin(), x.end()
#define rall(x) x.rbegin(), x.rend()
#define rev(x) reverse(x.begin(), x.end())
#define mset(a, b) memset(a, b, sizeof(a))
#define mcpy(a, b) memcpy(a, b, sizeof(a))
#define fo0(i, n) for (int i = 0, i##end = n; i < i##end; i++)
#define fo1(i, n) for (int i = 1, i##end = n; i <= i##end; i++)
#define fo(i, a, b) for (int i = a, i##end = b; i <= i##end; i++)
#define foe(i, x) for (__typeof((x).end()) i = (x).begin(); i != (x).end(); ++i)
#define fre(i, x)                                                              \
  for (__typeof((x).rend()) i = (x).rbegin(); i != (x).rend(); ++i)
#define fast                                                                   \
  ios_base::sync_with_stdio(false);                                            \
  cin.tie(0);                                                                  \
  cout.tie(0)
int gcd(int a, int b) { return b ? gcd(b, a % b) : a; }
const int inf = 1e18;
const int mod = 1e9 + 7;
const int N = 2e5 + 9;
void read_And_write() {
#ifndef ONLINE_JUDGE
  freopen("input.txt", "r", stdin);
  freopen("output.txt", "w", stdout);
#endif
}

void raushan_kumar() {
  int d = 0, e = 0, f = 0, g = 0, p = 0, w = 0, flag = 0, ans = 0, res = 0,
      cnt = 0, sum = 0;
  double f1 = 0.0, f2 = 0.0, f3 = 0.0;
  int n;
  cin >> n;
  n *= 2;
  int a[n];
  fo0(i, n) cin >> a[i];
  sort(a, a + n);

  for (int i = 0; i < n; i += 2)
    sum += a[i];
  cout << sum;
}

int32_t main() {
  fast;
  int t = 1;
  // cin>>t;
  while (t--) {
    raushan_kumar();
  }
}