Problem:
Score : 100 points

Problem Statement

Decades have passed since the beginning of AtCoder Beginner Contest.

The contests are labeled as ABC001, ABC002, ... from the first round, but after the 999-th round ABC999, a problem occurred: how the future rounds should be labeled?

In the end, the labels for the rounds from the 1000-th to the 1998-th are decided: ABD001, ABD002, ..., ABD999.

You are given an integer N between 1 and 1998 (inclusive). Print the first three characters of the label of the N-th round of AtCoder Beginner Contest.

Constraints

1 \leq N \leq 1998

N is an integer.

Input

Input is given from Standard Input in the following format:

N

Output

Print the first three characters of the label of the N-th round of AtCoder Beginner Contest.

Sample Input 1

999

Sample Output 1

ABC

The 999-th round of AtCoder Beginner Contest is labeled as ABC999.

Sample Input 2

1000

Sample Output 2

ABD

The 1000-th round of AtCoder Beginner Contest is labeled as ABD001.

Sample Input 3

1481

Sample Output 3

ABD

The 1481-th round of AtCoder Beginner Contest is labeled as ABD482.

Solution in C# (Mono 4.6.2.0) (judge verdict: Accepted)

using System;
using System.Linq;
using System.Collections;
using System.Collections.Generic;
using static System.Console;
class Program
{
    static void Main()
    {
        //入力
        //int[] input = Console.ReadLine().Split().Select(i => int.Parse(i)).ToArray();
        //string input= Console.ReadLine();
        int input =int.Parse(Console.ReadLine());
        Console.WriteLine(input<1000?"ABC":"ABD");


        /*
        //処理速度計測
        var sw = new System.Diagnostics.Stopwatch();
        sw.Start();
        //解法
 
        //処理速度表示
        sw.Stop();
        TimeSpan ts = sw.Elapsed;
        Console.WriteLine((int)(Math.Floor((ts).TotalMilliseconds))+"ms");
        */
        Console.ReadLine();

    }
}