Problem p02983 (C++)

Buggy submission (status: Time Limit Exceeded):
#include <algorithm>
#include <bits/stdc++.h>
#include <cctype>
#include <cmath>
#include <cstdio>
#include <cstring>
#include <functional>
#include <iostream>
#include <list>
#include <map>
#include <queue>
#include <set>
#include <sstream>
#include <stack>
#include <string>
#include <vector>
using namespace std;
#define DEBUG(x) cout << '>' << #x << ':' << x << endl;
#define REP(i, n) for (int i = 0; i < (n); i++)
#define FOR(i, a, b) for (int i = (a); i <= (b); i++)
#define FORD(i, a, b) for (int i = (a); i >= (b); i--)
inline bool EQ(double a, double b) { return fabs(a - b) < 1e-9; }
const int INF = 1 << 29;
typedef long long int ll;
inline int two(int n) { return 1 << n; }
inline int test(int n, int b) { return (n >> b) & 1; }
inline void set_bit(int &n, int b) { n |= two(b); }
inline void unset_bit(int &n, int b) { n &= ~two(b); }
inline int last_bit(int n) { return n & (-n); }
inline int ones(int n) {
  int res = 0;
  while (n && ++res)
    n -= n & (-n);
  return res;
}
template <class T> void chmax(T &a, const T &b) { a = max(a, b); }
template <class T> void chmin(T &a, const T &b) { a = min(a, b); }
const int MOD = 1000000007;

bool isPowerOfTwo(ll x) { return x && (!(x & (x - 1))); }
bool isPrime(int n) {
  if (n <= 1)
    return false;
  if (n <= 3)
    return true;
  if (n % 2 == 0 || n % 3 == 0)
    return false;

  for (int i = 5; i * i <= n; i = i + 6)
    if (n % i == 0 || n % (i + 2) == 0)
      return false;

  return true;
}
int highestPowerof2(unsigned int n) {
  // Invalid input
  if (n < 1)
    return 0;

  int res = 1;
  for (int i = 0; i < 8 * sizeof(unsigned int); i++) {
    int curr = 1 << i;
    if (curr > n)
      break;

    res = curr;
  }

  return res;
}
long long binpow(long long a, long long b) {
  long long res = 1;
  while (b > 0) {
    if (b & 1)
      res = res * a;
    a = a * a;
    b >>= 1;
  }
  return res;
}
////////////////////////////////////////////////////////////////////

int main() {
  ios_base::sync_with_stdio(false);
  cin.tie(NULL);
  cout.tie(NULL);
  int t = 1;
  while (t--) {
    ll l, r;
    cin >> l >> r;
    bool flag = false;
    ll mn = INT64_MAX;
    for (ll i = l; i < r; i++) {
      for (ll j = l + 1; j <= r; j++) {
        ll c = ((i % 2019) * (j % 2019)) % 2019;
        if (c == 0) {
          flag = true;
          break;
        }
        mn = min(mn, c);
      }
    }
    if (flag)
      cout << 0;
    else
      cout << mn;
  }
  return 0;
}

Fixed submission:
#include <algorithm>
#include <bits/stdc++.h>
#include <cctype>
#include <cmath>
#include <cstdio>
#include <cstring>
#include <functional>
#include <iostream>
#include <list>
#include <map>
#include <queue>
#include <set>
#include <sstream>
#include <stack>
#include <string>
#include <vector>
using namespace std;
#define DEBUG(x) cout << '>' << #x << ':' << x << endl;
#define REP(i, n) for (int i = 0; i < (n); i++)
#define FOR(i, a, b) for (int i = (a); i <= (b); i++)
#define FORD(i, a, b) for (int i = (a); i >= (b); i--)
inline bool EQ(double a, double b) { return fabs(a - b) < 1e-9; }
const int INF = 1 << 29;
typedef long long int ll;
inline int two(int n) { return 1 << n; }
inline int test(int n, int b) { return (n >> b) & 1; }
inline void set_bit(int &n, int b) { n |= two(b); }
inline void unset_bit(int &n, int b) { n &= ~two(b); }
inline int last_bit(int n) { return n & (-n); }
inline int ones(int n) {
  int res = 0;
  while (n && ++res)
    n -= n & (-n);
  return res;
}
template <class T> void chmax(T &a, const T &b) { a = max(a, b); }
template <class T> void chmin(T &a, const T &b) { a = min(a, b); }
const int MOD = 1000000007;

bool isPowerOfTwo(ll x) { return x && (!(x & (x - 1))); }
bool isPrime(int n) {
  if (n <= 1)
    return false;
  if (n <= 3)
    return true;
  if (n % 2 == 0 || n % 3 == 0)
    return false;

  for (int i = 5; i * i <= n; i = i + 6)
    if (n % i == 0 || n % (i + 2) == 0)
      return false;

  return true;
}
int highestPowerof2(unsigned int n) {
  // Invalid input
  if (n < 1)
    return 0;

  int res = 1;
  for (int i = 0; i < 8 * sizeof(unsigned int); i++) {
    int curr = 1 << i;
    if (curr > n)
      break;

    res = curr;
  }

  return res;
}
long long binpow(long long a, long long b) {
  long long res = 1;
  while (b > 0) {
    if (b & 1)
      res = res * a;
    a = a * a;
    b >>= 1;
  }
  return res;
}
////////////////////////////////////////////////////////////////////

int main() {
  ios_base::sync_with_stdio(false);
  cin.tie(NULL);
  cout.tie(NULL);
  int t = 1;
  while (t--) {
    ll l, r;
    cin >> l >> r;
    bool flag = false;
    ll mn = INT64_MAX;
    for (ll i = l; i < r; i++) {
      for (ll j = l + 1; j <= r; j++) {
        ll c = ((i % 2019) * (j % 2019)) % 2019;
        if (c == 0) {
          flag = true;
          break;
        }
        mn = min(mn, c);
      }
      if (flag)
        break;
    }
    if (flag)
      cout << 0;
    else
      cout << mn;
  }
  return 0;
}