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: Wrong Answer)

package main

import (
	"bufio"
	"fmt"
	"os"
	"strconv"
)

var scanner = bufio.NewScanner(os.Stdin)

func next() string {
	scanner.Scan()
	return scanner.Text()
}

func nextInt() int {
	i, _ := strconv.Atoi(next())
	return i
}

func main() {
	scanner.Split(bufio.ScanWords)

	l := nextInt()
	r := nextInt()

	if r-l >= 2018 {
		fmt.Println(0)
	} else {
		for i := l; i <= r; i++ {
			if i%2019 == 0 {
				fmt.Println(0)
				return
			}
		}
		fmt.Println((l * (l + 1)) % 2019)
	}
}