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 ConsoleApp34 {
    class Program {
        static void Main(string[] args) {
            int N = int.Parse(Console.ReadLine());

            if (N <= 999) {
                //if (N <= 9) {
                //    Console.WriteLine("ABC" + "00" + N);
                //} else if (N <= 99) {
                //    Console.WriteLine("ABC" + "0" + N);
                //} else {
                //    Console.WriteLine("ABC" + "" + N);
                //}
                Console.WriteLine("ABC");
            } else {
                //if (N - 999 <= 9) {
                //    Console.WriteLine("ABD" + "00" + (N - 999));
                //} else if (N - 999 <= 99) {
                //    Console.WriteLine("ABD" + "0" + (N - 999));
                //} else {
                //    Console.WriteLine("ABD" + "" + (N - 999));
                //}
                Console.WriteLine("ABD");
            }

        }

    }
}