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 C++14 (GCC 5.4.1) (judge verdict: Accepted)

#include <iostream>
#include <vector>
#include <algorithm>
#include <cmath>
#include <queue>
#include <limits>
#include <cassert>
#include <random>
#include <stack>
#include <ctime>
#define REP(i,n) for(long (i)=0;(i)<(n);(i)++)
#define REPI(i,a,b) for(long (i)=(a);(i)<(b);(i)++)
#define INF numeric_limits<double>::infinity()
constexpr long MOD = 1e9 + 7;
using namespace std;
using P = pair<long, long>;
using VI = vector<long>;

int main() {
    int d;
    cin >> d;
    if (d < 1000) {
        cout << "ABC" << endl;
 //       printf("%03d\n", d);
    } else {
        cout << "ABD" << endl;
//        printf("%03d\n", d - 1000 + 1);
    }
}