Problem:
Score : 300 points

Problem Statement

You are given two non-negative integers L and R.
We will choose two integers i and j such that L \leq i < j \leq R.
Find the minimum possible value of (i \times j) \mbox{ mod } 2019.

Constraints

All values in input are integers.

0 \leq L < R \leq 2 \times 10^9

Input

Input is given from Standard Input in the following format:

L R

Output

Print the minimum possible value of (i \times j) \mbox{ mod } 2019 when i and j are chosen under the given condition.

Sample Input 1

2020 2040

Sample Output 1

2

When (i, j) = (2020, 2021), (i \times j) \mbox{ mod } 2019 = 2.

Sample Input 2

4 5

Sample Output 2

20

We have only one choice: (i, j) = (4, 5).

Solution in C# (Mono 4.6.2.0) (judge verdict: Wrong Answer)

using System;
using System.Collections;
using System.Collections.Generic;
using System.Globalization;
using System.Linq;
using System.Numerics;
using System.Text;
using System.Threading;
using System.Threading.Tasks;
using System.Xml.Schema;
using static System.Console;

namespace ConsoleApp2
{
    class Program
    {
        static public int[] Sarray() { return ReadLine().Split().Select(int.Parse).ToArray(); }
        static public List<int> Slist() { return new List<int>(ReadLine().Split().Select(int.Parse)); }
        static void Main(string[] args)
        {
            var LR = Sarray();
            var L = LR[0];
            var R = LR[1];
            var table = new HashSet<int>();
            var min = int.MaxValue;
            for(var i=L;i<R;i++)
            {
                for(var j=i+1;j<=R;j++)
                {
                    var tmp = (i * j) % 2019;
                    if (table.Contains(tmp)) break;
                    table.Add(tmp);
                    if (tmp < min) min = tmp;
                    if (min == 0) break;
                }
            }
            WriteLine(min);
        }
    }
}