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)

struct MyIo{

}

impl MyIo{
    fn readline()->Vec<String>{
        let mut buf = String::new();
        std::io::stdin().read_line(&mut buf).unwrap();
        let ret:Vec<String> = buf.split_whitespace().map(|c|c.to_string()).collect();
        ret
    }
}


fn main() {

    let mut input = MyIo::readline().into_iter();

    let v = input.next().unwrap().parse::<i32>().unwrap();

    let result = 
    match v {
        0...999=>{"ABC"},
        _=>{"ABD"},
    };

    println!("{}",result);
}