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 JavaScript (node.js v5.12) (judge verdict: Accepted)

"use strict"
function Main(input) {
    if (!input.match(/([\n])/)){
        input = input.split(" ");
    } else {
        input = input.split("\n");
        for (var i = 0; i < input.length; i++){
            input[i] = input[i].split(" ");
        }
    }
    //中身↓
    let end = "D";
    if(input[0]<=999){
        end = "C";
    }
    console.log("AB"+end);
}
Main(require("fs").readFileSync("/dev/stdin", "utf8"));