Problem p02983 (C++)

Buggy submission (status: Time Limit Exceeded):
#include <bits/stdc++.h>
using namespace std;
using ll = long long;
#define INT(...)                                                               \
  int __VA_ARGS__;                                                             \
  in(__VA_ARGS__)
#define LL(...)                                                                \
  ll __VA_ARGS__;                                                              \
  in(__VA_ARGS__)
#define ULL(...)                                                               \
  ull __VA_ARGS__;                                                             \
  in(__VA_ARGS__)
#define STR(...)                                                               \
  string __VA_ARGS__;                                                          \
  in(__VA_ARGS__)
#define CHR(...)                                                               \
  char __VA_ARGS__;                                                            \
  in(__VA_ARGS__)
#define DBL(...)                                                               \
  double __VA_ARGS__;                                                          \
  in(__VA_ARGS__)
#define vec(type, name, ...) vector<type> name(__VA_ARGS__)
#define VEC(type, name, size)                                                  \
  vector<type> name(size);                                                     \
  in(name)
#define vv(type, name, h, ...)                                                 \
  vector<vector<type>> name(h, vector<type>(__VA_ARGS__))
#define VV(type, name, h, ...)                                                 \
  vector<vector<type>> name(h, vector<type>(__VA_ARGS__));                     \
  in(name)
#define vvv(type, name, h, w, ...)                                             \
  vector<vector<vector<type>>> name(                                           \
      h, vector<vector<type>>(w, vector<type>(__VA_ARGS__)))
inline int scan() { return getchar(); }
inline void scan(int &a) { scanf("%d", &a); }
inline void scan(unsigned &a) { scanf("%u", &a); }
inline void scan(long &a) { scanf("%ld", &a); }
inline void scan(long long &a) { scanf("%lld", &a); }
inline void scan(unsigned long long &a) { scanf("%llu", &a); }
inline void scan(char &a) { cin >> a; }
inline void scan(float &a) { scanf("%f", &a); }
inline void scan(double &a) { scanf("%lf", &a); }
inline void scan(long double &a) { scanf("%Lf", &a); }
inline void scan(vector<bool> &vec) {
  for (unsigned i = 0; i < vec.size(); i++) {
    int a;
    scan(a);
    vec[i] = a;
  }
}
inline void scan(string &a) { cin >> a; }
template <class T> inline void scan(vector<T> &vec);
template <class T, size_t size> inline void scan(array<T, size> &vec);
template <class T, class L> inline void scan(pair<T, L> &p);
template <class T, size_t size> inline void scan(T (&vec)[size]);
template <class T> inline void scan(vector<T> &vec) {
  for (auto &i : vec)
    scan(i);
}
template <class T, size_t size> inline void scan(array<T, size> &vec) {
  for (auto &i : vec)
    scan(i);
}
template <class T, class L> inline void scan(pair<T, L> &p) {
  scan(p.first);
  scan(p.second);
}
template <class T, size_t size> inline void scan(T (&vec)[size]) {
  for (auto &i : vec)
    scan(i);
}
template <class T> inline void scan(T &a) { cin >> a; }
inline void in() {}
template <class Head, class... Tail> inline void in(Head &head, Tail &...tail) {
  scan(head);
  in(tail...);
}
template <class T> inline bool chmax(T &a, T b) {
  if (a < b) {
    a = b;
    return 1;
  }
  return 0;
}
template <class T> inline bool chmin(T &a, T b) {
  if (a > b) {
    a = b;
    return 1;
  }
  return 0;
}
using Graph = vector<vector<int>>;
/* 4方向への隣接頂点への移動を表すベクトル */
const int dx[4] = {1, 0, -1, 0};
const int dy[4] = {0, 1, 0, -1};

const long long INF = 1LL << 60;
int main() {
  LL(L);
  LL(R);

  if (L - R >= 2020) {
    cout << 0 << endl;
    return 0;
  } else {
    ll ans = 2018;
    for (ll i = L; i <= R; ++i) {
      for (ll j = i + 1; j <= R; ++j) {
        ll tmp = i * j % 2019;
        ans = min(ans, tmp);
      }
    }
    cout << ans << endl;
  }
}

Fixed submission:
#include <bits/stdc++.h>
using namespace std;
using ll = long long;
#define INT(...)                                                               \
  int __VA_ARGS__;                                                             \
  in(__VA_ARGS__)
#define LL(...)                                                                \
  ll __VA_ARGS__;                                                              \
  in(__VA_ARGS__)
#define ULL(...)                                                               \
  ull __VA_ARGS__;                                                             \
  in(__VA_ARGS__)
#define STR(...)                                                               \
  string __VA_ARGS__;                                                          \
  in(__VA_ARGS__)
#define CHR(...)                                                               \
  char __VA_ARGS__;                                                            \
  in(__VA_ARGS__)
#define DBL(...)                                                               \
  double __VA_ARGS__;                                                          \
  in(__VA_ARGS__)
#define vec(type, name, ...) vector<type> name(__VA_ARGS__)
#define VEC(type, name, size)                                                  \
  vector<type> name(size);                                                     \
  in(name)
#define vv(type, name, h, ...)                                                 \
  vector<vector<type>> name(h, vector<type>(__VA_ARGS__))
#define VV(type, name, h, ...)                                                 \
  vector<vector<type>> name(h, vector<type>(__VA_ARGS__));                     \
  in(name)
#define vvv(type, name, h, w, ...)                                             \
  vector<vector<vector<type>>> name(                                           \
      h, vector<vector<type>>(w, vector<type>(__VA_ARGS__)))
inline int scan() { return getchar(); }
inline void scan(int &a) { scanf("%d", &a); }
inline void scan(unsigned &a) { scanf("%u", &a); }
inline void scan(long &a) { scanf("%ld", &a); }
inline void scan(long long &a) { scanf("%lld", &a); }
inline void scan(unsigned long long &a) { scanf("%llu", &a); }
inline void scan(char &a) { cin >> a; }
inline void scan(float &a) { scanf("%f", &a); }
inline void scan(double &a) { scanf("%lf", &a); }
inline void scan(long double &a) { scanf("%Lf", &a); }
inline void scan(vector<bool> &vec) {
  for (unsigned i = 0; i < vec.size(); i++) {
    int a;
    scan(a);
    vec[i] = a;
  }
}
inline void scan(string &a) { cin >> a; }
template <class T> inline void scan(vector<T> &vec);
template <class T, size_t size> inline void scan(array<T, size> &vec);
template <class T, class L> inline void scan(pair<T, L> &p);
template <class T, size_t size> inline void scan(T (&vec)[size]);
template <class T> inline void scan(vector<T> &vec) {
  for (auto &i : vec)
    scan(i);
}
template <class T, size_t size> inline void scan(array<T, size> &vec) {
  for (auto &i : vec)
    scan(i);
}
template <class T, class L> inline void scan(pair<T, L> &p) {
  scan(p.first);
  scan(p.second);
}
template <class T, size_t size> inline void scan(T (&vec)[size]) {
  for (auto &i : vec)
    scan(i);
}
template <class T> inline void scan(T &a) { cin >> a; }
inline void in() {}
template <class Head, class... Tail> inline void in(Head &head, Tail &...tail) {
  scan(head);
  in(tail...);
}
template <class T> inline bool chmax(T &a, T b) {
  if (a < b) {
    a = b;
    return 1;
  }
  return 0;
}
template <class T> inline bool chmin(T &a, T b) {
  if (a > b) {
    a = b;
    return 1;
  }
  return 0;
}
using Graph = vector<vector<int>>;
/* 4方向への隣接頂点への移動を表すベクトル */
const int dx[4] = {1, 0, -1, 0};
const int dy[4] = {0, 1, 0, -1};

const long long INF = 1LL << 60;
int main() {
  LL(L);
  LL(R);

  if (R - L >= 2020) {
    cout << 0 << endl;
    return 0;
  } else {
    ll ans = 2018;
    for (ll i = L; i <= R; ++i) {
      for (ll j = i + 1; j <= R; ++j) {
        ll tmp = i * j % 2019;
        ans = min(ans, tmp);
      }
    }
    cout << ans << endl;
  }
}