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 Python (3.8.2) (judge verdict: Accepted)

# A - ABD
# コンテスト名が開催数によって変化する
# 1~999 回目 ABC001 ABC002 ... ABC999
# 1000 ~ 1998 回目 ABD001 ABD002 ... ABD999
# 最初の3文字を出力させる

# 開催数 N (整数） の入力
N = int(input())
# print(N)

# 条件分岐　N が 1 ~ 999 の時 ABC
if N <= 999:
    answer = 'ABC'
elif N <= 1998:
    answer = 'ABD'

# 結果の表示
print(answer)