Problem p02983 (C++)

Buggy submission (status: Time Limit Exceeded):
#include <bits/stdc++.h>

#define FOR(i, a, b) for (int i = (a); i < (b); ++i)
#define REP(i, n) for (int i = 0; i < (n); ++i)
#define REPr(i, n) for (int i = (n)-1; i >= 0; --i)
#define FORq(i, m, n) for (int i = (m); i <= (n); ++i)
#define FORqr(i, m, n) for (int i = (n); i >= (m); --i)
#define PB push_back
#define MP make_pair
#define DEBUG printf("%s\n", "debug")
#define fst first
#define snd second
#define SIN(x, S) (S.count(x) != 0)
#define M0(x) memset(x, 0, sizeof(x))
#define FILL(x, y) memset(x, y, sizeof(x))
#define MM(x) memset(x, -1, sizeof(x))
#define ALL(x) (x).begin(), (x).end()
#define SCD(n) scanf("%d", &n)
#define SCD2(m, n) scanf("%d%d", &m, &n)
#define SCD3(m, n, k) scanf("%d%d%d", &m, &n, &k)
#define SCLLD(n) scanf("%lld", &n)
#define SCLLD2(m, n) scanf("%lld%lld", &m, &n)
#define SCLLD3(m, n, k) scanf("%lld%lld%lld", &m, &n, &k)
using namespace std;
typedef pair<int, int> PII;
typedef pair<long long, long long> PLL;
typedef vector<int> VI;
typedef vector<VI> VVI;
typedef vector<long long> VL;
typedef long long ll;
typedef long long integer;
///////////////////////////////////////////////
const ll MOD = 1e9 + 7;

ll gcd(ll x, ll y) { return y ? gcd(y, x % y) : x; }

template <class T> inline bool chmin(T &a, T b) {
  if (a > b) {
    a = b;
    return true;
  }
  return false;
}

template <class T> inline bool chmax(T &a, T b) {
  if (a < b) {
    a = b;
    return true;
  }
  return false;
}
///////////////////////////////////////////////
/*⁽⁽(ી₍₍⁽⁽(ી( ˆεˆ )ʃ)₎₎⁾⁾ʃ)₎₎*/
int main() {
  ll L, R;
  ll L2, R2;
  cin >> L >> R;
  L2 = (L - 1) / 2019;
  R2 = R / 2019;
  if (L2 != R2) {
    cout << 0 << endl;
  }

  ll ans = 1e16;
  FORq(i, L, R) {
    FORq(j, L, R) {
      if (i == j)
        continue;
      chmin(ans, ((ll)i * (ll)j) % 2019);
    }
  }

  cout << ans << "\n";
  return 0;
}


Fixed submission:
#include <bits/stdc++.h>

#define FOR(i, a, b) for (int i = (a); i < (b); ++i)
#define REP(i, n) for (int i = 0; i < (n); ++i)
#define REPr(i, n) for (int i = (n)-1; i >= 0; --i)
#define FORq(i, m, n) for (int i = (m); i <= (n); ++i)
#define FORqr(i, m, n) for (int i = (n); i >= (m); --i)
#define PB push_back
#define MP make_pair
#define DEBUG printf("%s\n", "debug")
#define fst first
#define snd second
#define SIN(x, S) (S.count(x) != 0)
#define M0(x) memset(x, 0, sizeof(x))
#define FILL(x, y) memset(x, y, sizeof(x))
#define MM(x) memset(x, -1, sizeof(x))
#define ALL(x) (x).begin(), (x).end()
#define SCD(n) scanf("%d", &n)
#define SCD2(m, n) scanf("%d%d", &m, &n)
#define SCD3(m, n, k) scanf("%d%d%d", &m, &n, &k)
#define SCLLD(n) scanf("%lld", &n)
#define SCLLD2(m, n) scanf("%lld%lld", &m, &n)
#define SCLLD3(m, n, k) scanf("%lld%lld%lld", &m, &n, &k)
using namespace std;
typedef pair<int, int> PII;
typedef pair<long long, long long> PLL;
typedef vector<int> VI;
typedef vector<VI> VVI;
typedef vector<long long> VL;
typedef long long ll;
typedef long long integer;
///////////////////////////////////////////////
const ll MOD = 1e9 + 7;

ll gcd(ll x, ll y) { return y ? gcd(y, x % y) : x; }

template <class T> inline bool chmin(T &a, T b) {
  if (a > b) {
    a = b;
    return true;
  }
  return false;
}

template <class T> inline bool chmax(T &a, T b) {
  if (a < b) {
    a = b;
    return true;
  }
  return false;
}
///////////////////////////////////////////////
/*⁽⁽(ી₍₍⁽⁽(ી( ˆεˆ )ʃ)₎₎⁾⁾ʃ)₎₎*/
int main() {
  ll L, R;
  ll L2, R2;
  cin >> L >> R;
  L2 = (L - 1) / 2019;
  R2 = R / 2019;
  if (L2 != R2) {
    cout << 0 << endl;
    return 0;
  }

  ll ans = 1e16;
  FORq(i, L, R) {
    FORq(j, L, R) {
      if (i == j)
        continue;
      chmin(ans, ((ll)i * (ll)j) % 2019);
    }
  }

  cout << ans << "\n";
  return 0;
}