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++ (GCC 9.2.1) (judge verdict: Accepted)

/*
 * cpp_filepath
 */

// C++ 14
#include <iostream>
#include <vector>
#include <algorithm>
#include <cmath>
#include <cstring> // memset
#include <cassert>
using namespace std;
#define ll long long
#define loop(__x, __start, __end) for(int __x = __start; __x < __end; __x++)
template <class T> ostream & operator << (ostream & out, vector<T> const & v) {
  for (auto &&a: v) out << a << " "; out << endl; return out;
}
template <class T> void dump(T &a) { cout << a << endl; }
void solve();
int main() { solve(); return 0; }


void solve() {
  int a; cin >> a;
  if (a < 1000) cout << "ABC" << endl;
  else cout << "ABD" << endl;
}