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 <bits/stdc++.h>
using namespace std;
#define ll long long int
#define fp(i,k) for(i=0;i<k;i++)
#define fm(i,k) for(i=k;i>=0;i--)
#define fr(i,j,k) for(i=j;i<k;i++)
#define pb push_back
#define vll vector<ll>
#define vst vector<string>
#define vch vector<char>
#define pii pair<ll,ll>
#define psi pair<string,ll>
#define pis pair<ll,string>
#define pci pair<char,ll>
#define pic pair<ll,char>
#define msi map<string,ll>
#define mci map<char,ll>
#define mis map<ll,string>
#define mic map<ll,char>
#define mii map<ll,ll>
#define mp make_pair
#define ld double
#define srt(v) sort(v.begin(),v.end())
#define rsrt(v) sort(v.begin(),v.end(),greater<ll>)
ll arr[1000005];
int main(){
    ios::sync_with_stdio(false);cin.tie(0);
    ll t,n,m,x,y,cnt1=0,f,cnt2=0,cnt3=0,i,j,k;
    cin>>n;
    if(n<=999 )cout<<"ABC\n";
    else cout<<"ABD\n";
    return 0;}