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 Rust (1.15.1) (judge verdict: Accepted)

use std::io;

macro_rules! parse_line {
    ($($t: ty),+) => ({
        let mut a_str = String::new();
        io::stdin().read_line(&mut a_str).expect("read error");
        let mut a_iter = a_str.split_whitespace();
        (
            $(
                a_iter.next().unwrap().parse::<$t>().expect("parse error"),
            )+
        )
    })
}

fn main() {
    let (n,) = parse_line!(u32);
    println!(
        "AB{}",
        if n < 1000 {
            "C"
        } else {
            "D"
        });
}