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 Rust (1.15.1) (judge verdict: Accepted)

use std::io::{stdin, stdout, BufReader, BufRead, StdinLock, Write, BufWriter};

fn main() {
    let (std_in, std_out) = (stdin(), stdout());
    let mut br = BufReader::new(std_in.lock());
    let mut bw = BufWriter::new(std_out.lock());
    
    let tmp = rvn::<usize>(&mut br);
    let (l, r) = (tmp[0], tmp[1]);
    let mut ans = 2019;
    for i in l..l+2020 {
        if i >= r {break;}
        for j in i+1..i+2021 {
            if j > r {break;}
            ans = std::cmp::min(ans, (i*j) % 2019);
        }
    }
    writeln!(&mut bw, "{}", ans);
}


//////////////////////////////////////////////////////////////////////////////////
#[allow(dead_code)]
fn rs(br: &mut BufReader<StdinLock>) -> Vec<char> {
    let mut buf = String::new();
    br.read_line(&mut buf).ok();
    buf.trim().chars().collect()
}

#[allow(dead_code)]
fn rn<T: std::str::FromStr>(br: &mut BufReader<StdinLock>) -> T {
    let mut buf = String::new();
    br.read_line(&mut buf).ok();
    buf.trim().parse().ok().unwrap()
}

#[allow(dead_code)]
fn rvs(br: &mut BufReader<StdinLock>) -> Vec<Vec<char>> {
    let mut buf = String::new();
    br.read_line(&mut buf).ok();
    buf.trim().split_whitespace().map(|e| e.chars().collect()).collect()
}

#[allow(dead_code)]
fn rvn<T: std::str::FromStr>(br: &mut BufReader<StdinLock>) -> Vec<T> {
    let mut buf = String::new();
    br.read_line(&mut buf).ok();
    buf.trim().split_whitespace().map(|e| e.parse().ok().unwrap()).collect()
}