Problem p04047 (C++)

Buggy submission (status: Runtime Error):
#define _CRT_SECURE_NO_WARNINGS
#define _USE_MATH_DEFINES

#include "bits/stdc++.h"
#define REP(i, a, b) for (i = a; i < b; ++i)
#define rep(i, n) REP(i, 0, n)
#define ll long long
#define ull unsigned ll
typedef long double ld;
#define ALL(a) (a).begin(), (a).end()
#define ifnot(a) if (not a)
#define dump(x) cerr << #x << " = " << (x) << endl
using namespace std;

void reader(int &a) { scanf("%d", &a); }
void reader(double &a) { scanf("%lf", &a); }
void reader(char a[]) { scanf("%s", a); }
void reader(char &a) { scanf(" %c", &a); }
void reader(ll &a) { scanf("%lld", &a); }
void reader(ull &a) { scanf("%llu", &a); }
// void reader(string& a){cin >> a;};
template <class T, class U> void reader(T &t, U &u) {
  reader(t);
  reader(u);
}
template <class T, class U, class V> void reader(T &t, U &u, V &v) {
  reader(t);
  reader(u);
  reader(v);
}

void writer(const int a, char c) {
  printf("%d", a);
  putchar(c);
}
void writer(const ll a, char c) {
  printf("%lld", a);
  putchar(c);
}
void writer(const ull a, char c) {
  printf("%llu", a);
  putchar(c);
}
void writer(const double a, char c) {
  printf("%.20lf", a);
  putchar(c);
}
void writer(const char a[]) { printf("%s", a); };
void writer(const char a[], char c) {
  printf("%s", a);
  putchar(c);
};
void writer(const char a, char c) {
  putchar(a);
  putchar(c);
};
template <class T> void writerLn(T t) { writer(t, '\n'); }
template <class T, class U> void writerLn(T t, U u) {
  writer(t, ' ');
  writer(u, '\n');
}
template <class T, class U, class V> void writerLn(T t, U u, V v) {
  writer(t, ' ');
  writer(u, ' ');
  writer(v, '\n');
}
template <class T> void writerArr(T x[], int n) {
  int i;
  if (!n) {
    putchar('\n');
    return;
  }
  rep(i, n - 1) writer(x[i], ' ');
  writer(x[n - 1], '\n');
}
template <class T> void writerVec(vector<T> x) {
  int n = x.size();
  int i;
  if (!n) {
    putchar('\n');
    return;
  }
  rep(i, n - 1) writer(x[i], ' ');
  writer(x[n - 1], '\n');
}

vector<string> split(const string &str, char sep) {
  vector<string> v;
  stringstream ss(str);
  string buffer;
  while (getline(ss, buffer, sep)) {
    v.push_back(buffer);
  }
  return v;
}
// #define int ll
bool test = 0;
int dx[] = {0, 1, 0, -1};
int dy[] = {1, 0, -1, 0};
#define INF (1 << 28)
ull mod = (int)1e9 + 7;
//.....................
#define MAX (int)1e6 + 5

signed main(void) {
  int i, j, k, l;
  ull N;
  ull L[100];
  cin >> N;
  rep(i, 2 * N) cin >> L[i];
  sort(L, L + 2 * N);
  int sum = 0;
  rep(i, N) { sum += min(L[i * 2], L[i * 2 + 1]); }
  cout << sum << endl;
  return 0;
}

Fixed submission:
#define _CRT_SECURE_NO_WARNINGS
#define _USE_MATH_DEFINES

#include "bits/stdc++.h"
#define REP(i, a, b) for (i = a; i < b; ++i)
#define rep(i, n) REP(i, 0, n)
#define ll long long
#define ull unsigned ll
typedef long double ld;
#define ALL(a) (a).begin(), (a).end()
#define ifnot(a) if (not a)
#define dump(x) cerr << #x << " = " << (x) << endl
using namespace std;

void reader(int &a) { scanf("%d", &a); }
void reader(double &a) { scanf("%lf", &a); }
void reader(char a[]) { scanf("%s", a); }
void reader(char &a) { scanf(" %c", &a); }
void reader(ll &a) { scanf("%lld", &a); }
void reader(ull &a) { scanf("%llu", &a); }
// void reader(string& a){cin >> a;};
template <class T, class U> void reader(T &t, U &u) {
  reader(t);
  reader(u);
}
template <class T, class U, class V> void reader(T &t, U &u, V &v) {
  reader(t);
  reader(u);
  reader(v);
}

void writer(const int a, char c) {
  printf("%d", a);
  putchar(c);
}
void writer(const ll a, char c) {
  printf("%lld", a);
  putchar(c);
}
void writer(const ull a, char c) {
  printf("%llu", a);
  putchar(c);
}
void writer(const double a, char c) {
  printf("%.20lf", a);
  putchar(c);
}
void writer(const char a[]) { printf("%s", a); };
void writer(const char a[], char c) {
  printf("%s", a);
  putchar(c);
};
void writer(const char a, char c) {
  putchar(a);
  putchar(c);
};
template <class T> void writerLn(T t) { writer(t, '\n'); }
template <class T, class U> void writerLn(T t, U u) {
  writer(t, ' ');
  writer(u, '\n');
}
template <class T, class U, class V> void writerLn(T t, U u, V v) {
  writer(t, ' ');
  writer(u, ' ');
  writer(v, '\n');
}
template <class T> void writerArr(T x[], int n) {
  int i;
  if (!n) {
    putchar('\n');
    return;
  }
  rep(i, n - 1) writer(x[i], ' ');
  writer(x[n - 1], '\n');
}
template <class T> void writerVec(vector<T> x) {
  int n = x.size();
  int i;
  if (!n) {
    putchar('\n');
    return;
  }
  rep(i, n - 1) writer(x[i], ' ');
  writer(x[n - 1], '\n');
}

vector<string> split(const string &str, char sep) {
  vector<string> v;
  stringstream ss(str);
  string buffer;
  while (getline(ss, buffer, sep)) {
    v.push_back(buffer);
  }
  return v;
}
// #define int ll
bool test = 0;
int dx[] = {0, 1, 0, -1};
int dy[] = {1, 0, -1, 0};
#define INF (1 << 28)
ull mod = (int)1e9 + 7;
//.....................
#define MAX (int)1e6 + 5

signed main(void) {
  int i, j, k, l;
  ull N;
  ull L[200];
  cin >> N;
  rep(i, 2 * N) cin >> L[i];
  sort(L, L + 2 * N);
  int sum = 0;
  rep(i, N) { sum += min(L[i * 2], L[i * 2 + 1]); }
  cout << sum << endl;
  return 0;
}