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)

/** MIT License Copyright (c) 2018 Vasilyev Daniil **/
#include <bits/stdc++.h>
#pragma GCC optimize("Ofast")
using namespace std;
template<typename T> using v=vector<T>;
#define int long long
typedef string str;
typedef vector<int> vint;
#define rep(a,l,r) for(int a=(l);a<(r);a++)
#define pb push_back
#define sz(a) ((int)(a).size())
const long long inf=4611686018427387903;//2^62-1
#if 0 //FileIO
ifstream fin ("input.txt" );
ofstream fout("output.txt");
#define get fin>>
#define put fout<<
#else
#define get cin>>
#define put cout<<
#endif
#define eol put endl
void read(){}             template<typename Arg,typename... Args> void read (Arg& arg,Args&... args){get   (arg)     ;read(args...) ;}
void print(){}            template<typename Arg,typename... Args> void print(Arg  arg,Args...  args){put   (arg)<<" ";print(args...);}
void debug(){cout<<endl;} template<typename Arg,typename... Args> void debug(Arg  arg,Args...  args){cout<<(arg)<<" ";debug(args...);}
int getInt(){int a; get a; return a;}
//code goes here
void run(){
    int n;
    get n;
    if (n<1000)put "ABC";
    else put "ABD";
}
int32_t main() {ios::sync_with_stdio(false);cin.tie(0);cout.tie(0);run();return 0;}