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 PHP (5.6.30) (judge verdict: Wrong Answer)

<?php

$k = trim(fgets(STDIN));

$dp = [];
$d = [1, 6, 9, 6**2, 6**3, 6**4, 6**5, 6**6, 6**7, 9, 9**1, 9**2, 9**3, 9**4, 9**5, 9**6];

$dp[0] = 0;

for ($i = 1;$i <= 1000000; $i++) $dp[$i] = 100000;

for ($i = 0;$i <= 100000; $i++) {
    foreach ($d as $v) {
        $dp[$i + $v] = $dp[$i] + 1 < $dp[$i + $v] ? $dp[$i] + 1 : $dp[$i + $v];
    }
}

echo $dp[$k];