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: Wrong Answer)

#include <bits/stdc++.h>
#define rep(var,cnt) for(int (var)=0; (var)<(int)(cnt); ++(var))
#define Rep(var,init,cnt) for(int (var)=(init); (var)<(cnt); ++(var))
#define ran(var,vec) for(auto &(var):(vec))
#define all(v) (v).begin(),(v).end()
#define rall(v) (v).rbegin(),(v).rend()
#define SORT(v) sort(all(v))
#define RSORT(v) sort(rall(v))
#define SUM(v) accumulate(all(v),0)
#define tget(tp,idx) get<idx>(tp)
#define TF(flag) (flag)?1:0
#define yn(f) cout<<(f?"yes":"no")<<endl
#define Yn(f) cout<<(f?"Yes":"No")<<endl
#define YN(f) cout<<(f?"YES":"NO")<<endl
#define COUT(x) cout<<(x)<<endl
using namespace std;

using ll = long long;
using ull = unsigned long long;
using pi = pair<int,int>;
using pl = pair<ll,ll>;
using ti = tuple<int,int,int>;
using tl = tuple<ll,ll,ll>;

template<typename T>
using vec = vector<T>;
template<typename T>
using mat = vector<vec<T>>;
template<typename T>
using cub = vector<mat<T>>;
template<typename T>
using val = valarray<T>;

template<typename T>
using pq = priority_queue<T>;
template<typename T>
using rpq = priority_queue<T,vec<T>,greater<T>>;

template<typename T1,typename T2>
ostream &operator<<(ostream &os, const pair<T1,T2> &p){
  os<<"P("<<p.first<<", "<<p.second<<") ";
  return os;
}

template<typename T1,typename T2>
istream &operator>>(istream &is, pair<T1,T2> &p){
  is>>p.first>>p.second;
  return is;
}

template<typename T>
ostream &operator<<(ostream &os, const vector<T> &v){
  cout<<"V{";
  for(int i=0; i<(int)v.size(); ++i){
    os<<v[i]<<(i+1!=v.size()?" ":"");
  }
  cout<<"}";
  return os;
}

template<typename T>
istream &operator>>(istream &is, vector<T> &v){
  for(T &in:v) is>>in;
  return is;
}

template<typename T>
ostream &operator<<(ostream &os, const valarray<T> &v){
  cout<<"V{";
  for(int i=0; i<(int)v.size(); ++i){
    os<<v[i]<<(i+1!=v.size()?" ":"");
  }
  cout<<"}";
  return os;
}

template<typename T>
istream &operator>>(istream &is, valarray<T> &v){
  for(T &in:v) is>>in;
  return is;
}

// Usual Template End ================================================

// Template End ======================================================

constexpr int MOD=1e9+7;

int main(void){
  int a; cin>>a;
  if(a>999) printf("ABD%03d",a-999);
  else printf("ABC%03d",a);
}