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 Go (1.6) (judge verdict: Accepted)

package main

import (
	"fmt"
	"os"
)

func main() {
	var a, b int
	fmt.Scan(&a, &b)
	mod := 2019

	if a*b < mod {
		fmt.Println(a * b)
		os.Exit(0)
	} else if a*b%mod == 0 {
		fmt.Println(0)
		os.Exit(0)
	}

	res := 2019
	for i := a; i <= b-1; i++ {
		for j := i + 1; j <= b; j++ {
			if m := i * j % mod; m < res {
				res = m
			}
			if res == 0 {
				break
			}
		}
		if res == 0 {
			break
		}
	}
	fmt.Println(res)
}