Problem p03767 (C++)

Buggy submission (status: Runtime Error):
// Zory-2019
#include <bits/stdc++.h>
using namespace std;
namespace mine {
typedef long long ll;
#define pii pair<int, int>
#define FR first
#define SE second
#define MP make_pair
#define PB push_back
#define vc vector
#define all(x) (x).begin(), (x).end()
#define sz(x) ((int)(x).size())
#define bin(x) (1ll << (x))
#define GG(x)                                                                  \
  if (x) {                                                                     \
    puts("error");                                                             \
    exit(666);                                                                 \
  }
#define fo(i, l, r) for (int i = (l), I = (r); i <= I; i++)
#define fd(i, r, l) for (int i = (r), I = (l); i >= I; i--)
ll qread() {
  ll ans = 0, f = 1;
  char c = getchar();
  while (c < '0' or c > '9') {
    if (c == '-')
      f = -1;
    c = getchar();
  }
  while ('0' <= c and c <= '9')
    ans = ans * 10 + c - '0', c = getchar();
  return ans * f;
}
void write(ll num) {
  if (num < 0)
    putchar('-'), num = -num;
  if (num >= 10)
    write(num / 10);
  putchar('0' + num % 10);
}
void write1(ll num) {
  write(num);
  putchar(' ');
}
void write2(ll num) {
  write(num);
  putchar('\n');
}
template <typename T> void chmax(T &x, const T y) { x = (x > y ? x : y); }
template <typename T> void chmin(T &x, const T y) { x = (x < y ? x : y); }
ll gcd(ll x, ll y) { return y ? gcd(y, x % y) : x; }

const int INF = 0x3f3f3f3f;
const int MOD = 1e9 + 7;
int mm(const int x) { return x >= MOD ? x - MOD : x; }
template <typename T> void add(T &x, const int &y) {
  x = (x + y >= MOD ? x + y - MOD : x + y);
}
ll qpower(ll x, ll e, int mod = MOD) {
  ll ans = 1;
  GG(e < 0) while (e) {
    if (e & 1)
      ans = ans * x % mod;
    x = x * x % mod;
    e >>= 1;
  }
  return ans;
}
ll invm(ll x) { return qpower(x, MOD - 2); }
const int N = 2e5 + 10;

int a[N];
void main() {
  int n = qread();
  fo(i, 1, n + n + n) a[i] = qread();
  sort(a + 1, a + n + n + n + 1);
  ll sum = 0;
  for (int i = n + 1; i <= n + n + n; i += 2)
    sum += a[i];
  write(sum);
}
}; // namespace mine
signed main() {
  srand(time(0));
  mine::main();
}


Fixed submission:
// Zory-2019
#include <bits/stdc++.h>
using namespace std;
namespace mine {
typedef long long ll;
#define pii pair<int, int>
#define FR first
#define SE second
#define MP make_pair
#define PB push_back
#define vc vector
#define all(x) (x).begin(), (x).end()
#define sz(x) ((int)(x).size())
#define bin(x) (1ll << (x))
#define GG(x)                                                                  \
  if (x) {                                                                     \
    puts("error");                                                             \
    exit(666);                                                                 \
  }
#define fo(i, l, r) for (int i = (l), I = (r); i <= I; i++)
#define fd(i, r, l) for (int i = (r), I = (l); i >= I; i--)
ll qread() {
  ll ans = 0, f = 1;
  char c = getchar();
  while (c < '0' or c > '9') {
    if (c == '-')
      f = -1;
    c = getchar();
  }
  while ('0' <= c and c <= '9')
    ans = ans * 10 + c - '0', c = getchar();
  return ans * f;
}
void write(ll num) {
  if (num < 0)
    putchar('-'), num = -num;
  if (num >= 10)
    write(num / 10);
  putchar('0' + num % 10);
}
void write1(ll num) {
  write(num);
  putchar(' ');
}
void write2(ll num) {
  write(num);
  putchar('\n');
}
template <typename T> void chmax(T &x, const T y) { x = (x > y ? x : y); }
template <typename T> void chmin(T &x, const T y) { x = (x < y ? x : y); }
ll gcd(ll x, ll y) { return y ? gcd(y, x % y) : x; }

const int INF = 0x3f3f3f3f;
const int MOD = 1e9 + 7;
int mm(const int x) { return x >= MOD ? x - MOD : x; }
template <typename T> void add(T &x, const int &y) {
  x = (x + y >= MOD ? x + y - MOD : x + y);
}
ll qpower(ll x, ll e, int mod = MOD) {
  ll ans = 1;
  GG(e < 0) while (e) {
    if (e & 1)
      ans = ans * x % mod;
    x = x * x % mod;
    e >>= 1;
  }
  return ans;
}
ll invm(ll x) { return qpower(x, MOD - 2); }
const int N = 3e5 + 10;

int a[N];
void main() {
  int n = qread();
  fo(i, 1, n + n + n) a[i] = qread();
  sort(a + 1, a + n + n + n + 1);
  ll sum = 0;
  for (int i = n + 1; i <= n + n + n; i += 2)
    sum += a[i];
  write(sum);
}
}; // namespace mine
signed main() {
  srand(time(0));
  mine::main();
}