Problem p02983 (C++)

Buggy submission (status: Time Limit Exceeded):
#pragma GCC optimize("O3")
#pragma GCC target("tune=native")
#pragma GCC target("avx")

#include <bits/stdc++.h>

// 汎用マクロ
#define ALL_OF(x) (x).begin(), (x).end()
#define REP(i, n) for (long long i = 0, i##_len = (n); i < i##_len; i++)
#define RANGE(i, is, ie)                                                       \
  for (long long i = (is), i##_end = (ie); i <= i##_end; i++)
#define DSRNG(i, is, ie)                                                       \
  for (long long i = (is), i##_end = (ie); i >= i##_end; i--)
#define UNIQUE(v)                                                              \
  {                                                                            \
    sort((v).begin(), (v).end());                                              \
    (v).erase(unique((v).begin(), (v).end()), (v).end());                      \
  }
template <class T> bool chmax(T &a, const T &b) {
  if (a < b) {
    a = b;
    return true;
  }
  return false;
}
template <class T> bool chmin(T &a, const T &b) {
  if (a > b) {
    a = b;
    return true;
  }
  return false;
}
#define INF 0x7FFFFFFF
#define LINF 0x7FFFFFFFFFFFFFFFLL
#define Yes(q) (q ? "Yes" : "No")
#define YES(q) (q ? "YES" : "NO")
#define DUMP(q)                                                                \
  cerr << "[DEBUG] " #q ": " << (q) << " at " __FILE__ ":" << __LINE__ << endl
#define DUMPALL(q)                                                             \
  {                                                                            \
    cerr << "[DEBUG] " #q ": [";                                               \
    REP(dumpall_i, (q).size()) {                                               \
      cerr << q[dumpall_i] << (dumpall_i == (q).size() - 1 ? "" : ", ");       \
    }                                                                          \
    cerr << "] at " __FILE__ ":" << __LINE__ << endl;                          \
  }
template <class T> T gcd(const T &a, const T &b) {
  return a < b ? gcd(b, a) : b ? gcd(b, a % b) : a;
}
template <class T> T lcm(const T &a, const T &b) { return a / gcd(a, b) * b; }

// gcc拡張マクロ
#define popcount __builtin_popcount
#define popcountll __builtin_popcountll

// エイリアス
using ll = long long;
using ull = unsigned long long;
using ld = long double;
using namespace std;

// モジュール

// 処理内容
int main() {

  ll l, r;
  cin >> l >> r;

  if (l - r + 1 >= 2019) {
    cout << 0 << endl;
    return 0;
  } else {
    ll ans = INF;
    RANGE(i, l, r) RANGE(j, i + 1, r) { chmin(ans, i * j % 2019); }
    cout << ans << endl;
  }
}

Fixed submission:
#pragma GCC optimize("O3")
#pragma GCC target("tune=native")
#pragma GCC target("avx")

#include <bits/stdc++.h>

// 汎用マクロ
#define ALL_OF(x) (x).begin(), (x).end()
#define REP(i, n) for (long long i = 0, i##_len = (n); i < i##_len; i++)
#define RANGE(i, is, ie)                                                       \
  for (long long i = (is), i##_end = (ie); i <= i##_end; i++)
#define DSRNG(i, is, ie)                                                       \
  for (long long i = (is), i##_end = (ie); i >= i##_end; i--)
#define UNIQUE(v)                                                              \
  {                                                                            \
    sort((v).begin(), (v).end());                                              \
    (v).erase(unique((v).begin(), (v).end()), (v).end());                      \
  }
template <class T> bool chmax(T &a, const T &b) {
  if (a < b) {
    a = b;
    return true;
  }
  return false;
}
template <class T> bool chmin(T &a, const T &b) {
  if (a > b) {
    a = b;
    return true;
  }
  return false;
}
#define INF 0x7FFFFFFF
#define LINF 0x7FFFFFFFFFFFFFFFLL
#define Yes(q) (q ? "Yes" : "No")
#define YES(q) (q ? "YES" : "NO")
#define DUMP(q)                                                                \
  cerr << "[DEBUG] " #q ": " << (q) << " at " __FILE__ ":" << __LINE__ << endl
#define DUMPALL(q)                                                             \
  {                                                                            \
    cerr << "[DEBUG] " #q ": [";                                               \
    REP(dumpall_i, (q).size()) {                                               \
      cerr << q[dumpall_i] << (dumpall_i == (q).size() - 1 ? "" : ", ");       \
    }                                                                          \
    cerr << "] at " __FILE__ ":" << __LINE__ << endl;                          \
  }
template <class T> T gcd(const T &a, const T &b) {
  return a < b ? gcd(b, a) : b ? gcd(b, a % b) : a;
}
template <class T> T lcm(const T &a, const T &b) { return a / gcd(a, b) * b; }

// gcc拡張マクロ
#define popcount __builtin_popcount
#define popcountll __builtin_popcountll

// エイリアス
using ll = long long;
using ull = unsigned long long;
using ld = long double;
using namespace std;

// モジュール

// 処理内容
int main() {

  ll l, r;
  cin >> l >> r;

  if (r - l + 1 >= 2019) {
    cout << 0 << endl;
    return 0;
  } else {
    ll ans = INF;
    RANGE(i, l, r) RANGE(j, i + 1, r) { chmin(ans, i * j % 2019); }
    cout << ans << endl;
  }
}