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 Common Lisp (SBCL 1.1.14) (judge verdict: Wrong Answer)

(let ((n (read))
      (a '())
      (ans 0))
  (loop for i from 1 while (<= (expt 6 i) n) do
        (setf a (append a (list (expt 6 i) (expt 9 i)))))
  (setf a (sort (copy-list a) #'>))
  (loop for i in a do
        (if (<= i n) (progn (incf ans (floor (/ n i)))
                           (setf n (rem n i)))))
  (format t "~A~%" (+ ans n)))