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.Collections.Generic;
using System.Linq;
using System.Text;
using System.Threading.Tasks;

namespace AtCoder
{
    class Program
    {
        static void Main(string[] args)
        {
            // 整数の入力
            int N = int.Parse(Console.ReadLine());
            // スペース区切りの整数の入力
            //string[] input = Console.ReadLine().Split(' ');
            //int a = int.Parse(input[0]);
            //int b = int.Parse(input[1]);
            //int c = int.Parse(input[2]);
            string rtn = "ABC";
            if (N>=1000)
            {
                rtn = "ABD";
            }
            
            // 文字列の入力
            //string s = Console.ReadLine();
            //string aaa ="Odd";
            //if (a%2==0 ||b%2==0)
            //{
            //    aaa = "Even";
            //}
            //出力
            Console.WriteLine(rtn);
            //Console.ReadKey();
        }
    }
}