Problem:
Score : 100 points

Problem Statement

We will buy a product for N yen (the currency of Japan) at a shop.

If we use only 1000-yen bills to pay the price, how much change will we receive?

Assume we use the minimum number of bills required.

Constraints

1 \leq N \leq 10000

N is an integer.

Input

Input is given from Standard Input in the following format:

N

Output

Print the amount of change as an integer.

Sample Input 1

1900

Sample Output 1

100

We will use two 1000-yen bills to pay the price and receive 100 yen in change.

Sample Input 2

3000

Sample Output 2

0

We can pay the exact price.

Solution in C# (.NET Core 3.1.201) (judge verdict: Wrong Answer)

using System;
using System.Diagnostics;
using System.IO;
using System.Text;
using System.Linq;
using System.Collections.Generic;
using System.Text.RegularExpressions;

class Program
{
    const string Yes = "Yes";
    const string No = "No";
    const char White = '.';
    const char Black = '#';
    const long Mod = 1000000007;

    static void Main(string[] args) {
        checked {
#if DEBUG
            MyDebugger.Test(process, "../TextFile1.txt");
            //TestCaseMaker.MakeTestCase1("../TextFile2.txt");
            //MyDebugger.Test(process, "../TextFile2.txt");
#else
            object ret = process(new StreamReader(Console.OpenStandardInput()));
            //Console.WriteLine(ret);
#endif
        }
    }

    static object process(TextReader input) {
        var n = int.Parse(input.ReadLine());

        var x = 1000 - (n % 1000);
        return x==1000 ? 0 : x;
    }

    static int[] ToIntArray(string strs, int n) {
        var ret = new int[n];
        if (n == 0) return ret;
        var spl = strs.Split(' ');
        for (int i = 0; i < n; i++)
            ret[i] = int.Parse(spl[i]);
        return ret;
    }
}