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 <climits>
#include <stack>
#include <queue>
#include <string>
#include <set>
#include <map>
#include <math.h>
#include <algorithm>
#include <vector>
#include <string.h>
#include <random>
#include <iomanip>
#include <limits>
 
using namespace std;
 
typedef long long ll;
 
typedef pair<ll,ll> P;
long long int INF = 1e18;
double Pi = 3.141592653589;
ll mod = 1000000007;
// memset(a,0,sizeof(a)); →全部０にする
 
vector<int> G[100005];
std::vector<P> tree[100010];
 
int dx[8]={1,0,-1,0,1,1,-1,-1};
int dy[8]={0,1,0,-1,1,-1,-1,1};
 
#define p(x) cout<<x<<endl;
#define el cout<<endl;
#define pe(x) cout<<x<<" ";
#define re(i,a,b) for(i=a;i<=b;i++)
 
ll i,j,k,l,ii,jj;
ll n,m,a,b,c,d,ans,num,sum;
ll x[100005],y[100005];
 
int main(){
    cin>>n; 
	if(n<=999){
		p("ABC");
	}else{
		p("ABD");
	}
    return 0;
}