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++14 (GCC 5.4.1) (judge verdict: Wrong Answer)

#include <algorithm>
#include <iostream>
#include <vector>
#include <queue>
#include <set>
#include <string>
#include <map>

#define rep(i, n) for (int i = 0; i < (n); ++i)
#define Rep(i, sta, n) for (int i = sta; i < n; ++i)

using namespace std;
typedef long long ll;
const int mod = 1000000007;

int main() {
    ll l, r;
    cin >> l >> r;
    if ((r - l) >= 2018) {
        cout << 0 << endl;
        return 0;
    }
    int ml, mr;
    mr = r % 2019;
    ml = l % 2019;

    int ans = 0;
    if (ml < mr) ans = ml * (ml + 1);
    else ans = 0;   
    cout << ans << endl;
    return 0;
}