Problem p02983 (C++)

Buggy submission (status: Time Limit Exceeded):
#define _CRT_SECURE_NO_WARNINGS
#include "bits/stdc++.h"
#if defined(_MSC_VER) || defined(ONLINE_JUDGE)
#define getchar_unlocked _getchar_nolock
#define putchar_unlocked _putchar_nolock
#endif
using namespace std;
#define rep(i, n) for (int i = 0; i < (n); ++i)
#define FOR(i, m, n) for (int i = (m); i < (n); ++i)
#define sz(x) ((int)(x).size())
#define all(x) (x).begin(), (x).end()
#define mp make_pair
#define pb push_back
#define dump(x) cerr << #x << " = " << (x) << endl;
using LL = long long;
using VS = vector<string>;
using VD = vector<double>;
using VI = vector<int>;
using VL = vector<LL>;
using VVI = vector<VI>;
using VVL = vector<VL>;
using PII = pair<int, int>;
using PLL = pair<LL, LL>;
const int inf = (int)1e9;
const double pi = acos(-1.0);
const LL MOD = 1000000007;
const string Snum = "0123456789";
const int dx[] = {-1, 0, 1, 0, -1, -1, 1, 1},
          dy[] = {0, 1, 0, -1, -1, 1, -1, 1};
template <class T> void Sort(T &a) { sort(a.begin(), a.end()); }
template <class T> void ReSort(T &a) { sort(a.rbegin(), a.rend()); }
template <class T> void Reverse(T &a) { reverse(a.begin(), a.end()); }
template <class T> void Unique(T &a) {
  a.erase(unique(a.begin(), a.end()), a.end());
}
template <class T> auto Max(const T &a) {
  return *max_element(a.begin(), a.end());
}
template <class T> auto Min(const T &a) {
  return *min_element(a.begin(), a.end());
}
template <class T, class U> int Count(const T &a, U c) {
  return count(a.begin(), a.end(), c);
}
template <class T, class U> U Sum(const T &a, U init = 0) {
  return accumulate(a.begin(), a.end(), init);
}
template <class T, class U> int Lower(const T &a, U s) {
  return lower_bound(a.begin(), a.end(), s) - a.begin();
}
template <class T, class U> int Upper(const T &a, U s) {
  return upper_bound(a.begin(), a.end(), s) - a.begin();
}
template <class T> T Age(T a, T b) { return (a + b - 1) / b; }
template <class T> T Gcd(T n, T m) { return m == 0 ? n : Gcd(m, n % m); }
template <class T> T Lcm(T n, T m) { return n / Gcd(n, m) * m; }

/* INPUT */
template <class T> T InputF() { return 0; }
template <> char InputF() {
  char ret = '\0', c = getchar_unlocked();
  while (c != '\0' && c != '\n' && c != '\t' && c != ' ') {
    ret = c;
    c = getchar_unlocked();
  }
  return ret;
}
template <> string InputF() {
  string ret;
  char c = getchar_unlocked();
  while (c != '\0' && c != '\n' && c != '\t' && c != ' ') {
    ret.push_back(c);
    c = getchar_unlocked();
  }
  return ret;
}
template <> int InputF() {
  int ret = 0;
  bool neg = false;
  char c = getchar_unlocked();
  if (c == '-') {
    neg = true;
    c = getchar_unlocked();
  }
  while ('0' <= c && c <= '9') {
    ret = ret * 10 + (c - '0');
    c = getchar_unlocked();
  }
  return neg ? -ret : ret;
}
template <> LL InputF() {
  LL ret = 0;
  bool neg = false;
  char c = getchar_unlocked();
  if (c == '-') {
    neg = true;
    c = getchar_unlocked();
  }
  while ('0' <= c && c <= '9') {
    ret = ret * 10LL + (LL(c) - LL('0'));
    c = getchar_unlocked();
  }
  return neg ? -ret : ret;
}
template <> double InputF() {
  double ret = 0, dp = 1;
  bool neg = false, adp = false;
  char c = getchar_unlocked();
  if (c == '-') {
    neg = true;
    c = getchar_unlocked();
  }
  while (('0' <= c && c <= '9') || c == '.') {
    if (c == '.') {
      adp = true;
    } else if (adp) {
      dp *= 0.1;
      ret += (c - '0') * dp;
    } else {
      ret = ret * 10.0 + (c - '0');
    }
    c = getchar_unlocked();
  }
  return neg ? -ret : ret;
}

template <class T> T StoT(string s) { return s; }
template <> char StoT(string s) { return s.front(); }
template <> string StoT(string s) { return s; }
template <> int StoT(string s) { return stoi(s); }
template <> LL StoT(string s) { return stoll(s); }
template <> double StoT(string s) { return stod(s); }

string GetLine() {
  string ret;
  char c = getchar_unlocked();
  while (c != '\0' && c != '\n') {
    ret.push_back(c);
    c = getchar_unlocked();
  }
  return ret;
}

VS InputB;
template <class T> struct InputC {
  operator T() { return InputF<T>(); }
  vector<T> operator[](int h) {
    vector<T> ret(h);
    rep(i, h) ret[i] = InputF<T>();
    return ret;
  }
  vector<vector<T>> operator[](PII p) {
    int h, w;
    tie(h, w) = p;
    vector<vector<T>> ret(h, vector<T>(w));
    rep(i, h) rep(j, w) ret[i][j] = InputF<T>();
    return ret;
  }
  T at(int n) {
    while (sz(InputB) <= n)
      InputB.pb(InputF<string>());
    return StoT<T>(InputB[n]);
  }
  vector<T> at(int n, int h) {
    vector<T> ret(h);
    rep(i, h) ret[i] = at(i + n);
    return ret;
  }
  vector<vector<T>> at(int n, int h, int w) {
    vector<vector<T>> ret(h, vector<T>(w));
    rep(i, h) rep(j, w) ret[i][j] = at(n + i * w + j);
    return ret;
  }
};
InputC<char> inc;
InputC<string> ins;
InputC<int> ini;
InputC<LL> inl;
InputC<double> ind;

/* OUTPUT */
class ostreamfbuff : public std::basic_streambuf<char, std::char_traits<char>> {
protected:
  int overflow(int nCh = EOF) {
    putchar_unlocked(nCh);
    return 0;
  }
};
class ostreamf : public std::basic_iostream<char, std::char_traits<char>> {
public:
  ostreamf(void)
      : std::basic_iostream<char, std::char_traits<char>>(new ostreamfbuff()) {}
};
ostreamf coutf;
ostream &operator<<(ostream &ostr, InputC<string> i) {
  ostr << string(i);
  return ostr;
}
struct BoolStr {
  string t, f;
  BoolStr(string tr, string fa) : t(tr), f(fa) {}
} yes("yes", "no"), Yes("Yes", "No"), YES("YES", "NO"), Yay("Yay!", ":(");
struct Divizer {
  string s;
  Divizer(string s_) : s(s_) {}
} spc(" "), nosp(""), comma(","), lin("\n");
struct Output {
  bool flag = false;
  BoolStr bs;
  Divizer di;
  Output(bool f, BoolStr b, Divizer d) : flag(f), bs(b), di(d) {}

  template <class T> void print(T o) { coutf << o; }
  void print(double o) { printf("%.20f", o); }
  void print(bool o) { coutf << (o ? bs.t : bs.f); }
  template <class T, class U> void print(const pair<T, U> &o) {
    print(o.first);
    coutf << di.s;
    print(o.second);
  }
  template <class T> void print(const vector<T> &o) {
    for (int i = 0; i < (int)o.size(); ++i) {
      if (i != 0)
        coutf << di.s;
      print(o[i]);
    }
  }
  template <class T, class U> void print(const map<T, U> &o) {
    coutf << "Map";
    for (auto a : o) {
      coutf << " {";
      print(a);
      coutf << "},";
    }
    coutf << "\n";
  }
  template <class T> void print(const set<T> &o) {
    coutf << "Set {";
    for (auto a : o) {
      print(a);
      coutf << ",";
    }
    coutf << "}\n";
  }
  template <class T> Output operator,(T o) {
    if (flag)
      coutf << di.s;
    print(o);
    Output t(true, bs, di);
    return t;
  }
  Output operator,(Output o) {
    coutf << '\n';
    return o;
  }
  Output operator,(BoolStr b) {
    Output t(flag, b, di);
    return t;
  }
  Output operator,(Divizer d) {
    Output t(flag, bs, d);
    return t;
  }
} out(false, Yes, spc);

/* ANSWER */
struct Answer {
  int mini = INT_MAX, maxi = INT_MIN, sumi = 0;
  LL minl = LLONG_MAX, maxl = LLONG_MIN, suml = 0;
  double mind = DBL_MAX, maxd = DBL_MIN, sumd = 0;
  int cnt = 0;
  void operator=(int n) {
    mini = min(mini, n);
    maxi = max(maxi, n);
    sumi += n;
    cnt++;
  }
  void operator=(LL n) {
    minl = min(minl, n);
    maxl = max(maxl, n);
    suml += n;
    cnt++;
  }
  void operator=(double n) {
    mind = min(mind, n);
    maxd = max(maxd, n);
    sumd += n;
    cnt++;
  }
} ans;

int main() {
  int L = ini, R = ini;
  int l = L % 2019, r = l + (R - L);
  FOR(i, l, r + 1) FOR(j, i + 1, r + 1) { ans = i * j % 2019; }
  out, ans.mini, out;
}

Fixed submission:
#define _CRT_SECURE_NO_WARNINGS
#include "bits/stdc++.h"
#if defined(_MSC_VER) || defined(ONLINE_JUDGE)
#define getchar_unlocked _getchar_nolock
#define putchar_unlocked _putchar_nolock
#endif
using namespace std;
#define rep(i, n) for (int i = 0; i < (n); ++i)
#define FOR(i, m, n) for (int i = (m); i < (n); ++i)
#define sz(x) ((int)(x).size())
#define all(x) (x).begin(), (x).end()
#define mp make_pair
#define pb push_back
#define dump(x) cerr << #x << " = " << (x) << endl;
using LL = long long;
using VS = vector<string>;
using VD = vector<double>;
using VI = vector<int>;
using VL = vector<LL>;
using VVI = vector<VI>;
using VVL = vector<VL>;
using PII = pair<int, int>;
using PLL = pair<LL, LL>;
const int inf = (int)1e9;
const double pi = acos(-1.0);
const LL MOD = 1000000007;
const string Snum = "0123456789";
const int dx[] = {-1, 0, 1, 0, -1, -1, 1, 1},
          dy[] = {0, 1, 0, -1, -1, 1, -1, 1};
template <class T> void Sort(T &a) { sort(a.begin(), a.end()); }
template <class T> void ReSort(T &a) { sort(a.rbegin(), a.rend()); }
template <class T> void Reverse(T &a) { reverse(a.begin(), a.end()); }
template <class T> void Unique(T &a) {
  a.erase(unique(a.begin(), a.end()), a.end());
}
template <class T> auto Max(const T &a) {
  return *max_element(a.begin(), a.end());
}
template <class T> auto Min(const T &a) {
  return *min_element(a.begin(), a.end());
}
template <class T, class U> int Count(const T &a, U c) {
  return count(a.begin(), a.end(), c);
}
template <class T, class U> U Sum(const T &a, U init = 0) {
  return accumulate(a.begin(), a.end(), init);
}
template <class T, class U> int Lower(const T &a, U s) {
  return lower_bound(a.begin(), a.end(), s) - a.begin();
}
template <class T, class U> int Upper(const T &a, U s) {
  return upper_bound(a.begin(), a.end(), s) - a.begin();
}
template <class T> T Age(T a, T b) { return (a + b - 1) / b; }
template <class T> T Gcd(T n, T m) { return m == 0 ? n : Gcd(m, n % m); }
template <class T> T Lcm(T n, T m) { return n / Gcd(n, m) * m; }

/* INPUT */
template <class T> T InputF() { return 0; }
template <> char InputF() {
  char ret = '\0', c = getchar_unlocked();
  while (c != '\0' && c != '\n' && c != '\t' && c != ' ') {
    ret = c;
    c = getchar_unlocked();
  }
  return ret;
}
template <> string InputF() {
  string ret;
  char c = getchar_unlocked();
  while (c != '\0' && c != '\n' && c != '\t' && c != ' ') {
    ret.push_back(c);
    c = getchar_unlocked();
  }
  return ret;
}
template <> int InputF() {
  int ret = 0;
  bool neg = false;
  char c = getchar_unlocked();
  if (c == '-') {
    neg = true;
    c = getchar_unlocked();
  }
  while ('0' <= c && c <= '9') {
    ret = ret * 10 + (c - '0');
    c = getchar_unlocked();
  }
  return neg ? -ret : ret;
}
template <> LL InputF() {
  LL ret = 0;
  bool neg = false;
  char c = getchar_unlocked();
  if (c == '-') {
    neg = true;
    c = getchar_unlocked();
  }
  while ('0' <= c && c <= '9') {
    ret = ret * 10LL + (LL(c) - LL('0'));
    c = getchar_unlocked();
  }
  return neg ? -ret : ret;
}
template <> double InputF() {
  double ret = 0, dp = 1;
  bool neg = false, adp = false;
  char c = getchar_unlocked();
  if (c == '-') {
    neg = true;
    c = getchar_unlocked();
  }
  while (('0' <= c && c <= '9') || c == '.') {
    if (c == '.') {
      adp = true;
    } else if (adp) {
      dp *= 0.1;
      ret += (c - '0') * dp;
    } else {
      ret = ret * 10.0 + (c - '0');
    }
    c = getchar_unlocked();
  }
  return neg ? -ret : ret;
}

template <class T> T StoT(string s) { return s; }
template <> char StoT(string s) { return s.front(); }
template <> string StoT(string s) { return s; }
template <> int StoT(string s) { return stoi(s); }
template <> LL StoT(string s) { return stoll(s); }
template <> double StoT(string s) { return stod(s); }

string GetLine() {
  string ret;
  char c = getchar_unlocked();
  while (c != '\0' && c != '\n') {
    ret.push_back(c);
    c = getchar_unlocked();
  }
  return ret;
}

VS InputB;
template <class T> struct InputC {
  operator T() { return InputF<T>(); }
  vector<T> operator[](int h) {
    vector<T> ret(h);
    rep(i, h) ret[i] = InputF<T>();
    return ret;
  }
  vector<vector<T>> operator[](PII p) {
    int h, w;
    tie(h, w) = p;
    vector<vector<T>> ret(h, vector<T>(w));
    rep(i, h) rep(j, w) ret[i][j] = InputF<T>();
    return ret;
  }
  T at(int n) {
    while (sz(InputB) <= n)
      InputB.pb(InputF<string>());
    return StoT<T>(InputB[n]);
  }
  vector<T> at(int n, int h) {
    vector<T> ret(h);
    rep(i, h) ret[i] = at(i + n);
    return ret;
  }
  vector<vector<T>> at(int n, int h, int w) {
    vector<vector<T>> ret(h, vector<T>(w));
    rep(i, h) rep(j, w) ret[i][j] = at(n + i * w + j);
    return ret;
  }
};
InputC<char> inc;
InputC<string> ins;
InputC<int> ini;
InputC<LL> inl;
InputC<double> ind;

/* OUTPUT */
class ostreamfbuff : public std::basic_streambuf<char, std::char_traits<char>> {
protected:
  int overflow(int nCh = EOF) {
    putchar_unlocked(nCh);
    return 0;
  }
};
class ostreamf : public std::basic_iostream<char, std::char_traits<char>> {
public:
  ostreamf(void)
      : std::basic_iostream<char, std::char_traits<char>>(new ostreamfbuff()) {}
};
ostreamf coutf;
ostream &operator<<(ostream &ostr, InputC<string> i) {
  ostr << string(i);
  return ostr;
}
struct BoolStr {
  string t, f;
  BoolStr(string tr, string fa) : t(tr), f(fa) {}
} yes("yes", "no"), Yes("Yes", "No"), YES("YES", "NO"), Yay("Yay!", ":(");
struct Divizer {
  string s;
  Divizer(string s_) : s(s_) {}
} spc(" "), nosp(""), comma(","), lin("\n");
struct Output {
  bool flag = false;
  BoolStr bs;
  Divizer di;
  Output(bool f, BoolStr b, Divizer d) : flag(f), bs(b), di(d) {}

  template <class T> void print(T o) { coutf << o; }
  void print(double o) { printf("%.20f", o); }
  void print(bool o) { coutf << (o ? bs.t : bs.f); }
  template <class T, class U> void print(const pair<T, U> &o) {
    print(o.first);
    coutf << di.s;
    print(o.second);
  }
  template <class T> void print(const vector<T> &o) {
    for (int i = 0; i < (int)o.size(); ++i) {
      if (i != 0)
        coutf << di.s;
      print(o[i]);
    }
  }
  template <class T, class U> void print(const map<T, U> &o) {
    coutf << "Map";
    for (auto a : o) {
      coutf << " {";
      print(a);
      coutf << "},";
    }
    coutf << "\n";
  }
  template <class T> void print(const set<T> &o) {
    coutf << "Set {";
    for (auto a : o) {
      print(a);
      coutf << ",";
    }
    coutf << "}\n";
  }
  template <class T> Output operator,(T o) {
    if (flag)
      coutf << di.s;
    print(o);
    Output t(true, bs, di);
    return t;
  }
  Output operator,(Output o) {
    coutf << '\n';
    return o;
  }
  Output operator,(BoolStr b) {
    Output t(flag, b, di);
    return t;
  }
  Output operator,(Divizer d) {
    Output t(flag, bs, d);
    return t;
  }
} out(false, Yes, spc);

/* ANSWER */
struct Answer {
  int mini = INT_MAX, maxi = INT_MIN, sumi = 0;
  LL minl = LLONG_MAX, maxl = LLONG_MIN, suml = 0;
  double mind = DBL_MAX, maxd = DBL_MIN, sumd = 0;
  int cnt = 0;
  void operator=(int n) {
    mini = min(mini, n);
    maxi = max(maxi, n);
    sumi += n;
    cnt++;
  }
  void operator=(LL n) {
    minl = min(minl, n);
    maxl = max(maxl, n);
    suml += n;
    cnt++;
  }
  void operator=(double n) {
    mind = min(mind, n);
    maxd = max(maxd, n);
    sumd += n;
    cnt++;
  }
} ans;

int main() {
  LL L = inl, R = inl, diff = R - L;
  LL l, r;

  if (L / 2019 == R / 2019) {
    l = L % 2019;
    r = R % 2019;
  } else {
    l = L % 2019;
    r = R % 2019 + 2019;
    if (r > R)
      r -= 2019;
  }

  LL Ans = 100000;
  for (LL i = l; i <= r; ++i)
    for (LL j = i + 1; j <= r; ++j) {
      Ans = min(Ans, i * j % 2019);
    }
  out, Ans, out;
}