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: Accepted)

using System;
using System.Text;
using System.Collections.Generic;
using System.Linq;
using System.Numerics;

class AtCoder
{
    const int MOD = 1000000007;
    public void Slove()
    {
        var inputs = Console.ReadLine().Split();
        int ln = int.Parse(inputs[0]);
        int rn = int.Parse(inputs[1]);
        int count = Math.Min(2019, rn - ln + 1);
        long ans = 2018;
        foreach(int num in Enumerable.Range(ln, count - 1))
            foreach(int num2 in Enumerable.Range(ln, count).Skip(ln - num + 1))
            {
                ans = Math.Min(ans, (long)num * num2 % 2019);
            }
        Console.WriteLine(ans);
    }
    static void Main()
    {
        var ac = new AtCoder();
        ac.Slove();
    }
}