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 <iomanip>
#include <string>
#include <sstream>
#include <vector>
#include <array>
#include <unordered_map>
#include <algorithm>
#include <numeric>
#include <set>
#include <map>
#include <queue>
#include <stack>
#include <bitset>
#include <valarray>
#include <utility>
#include <tuple>
#include <cmath>
#include <random>

using ll = long long;

//vector
template <class T>
using vec = std::vector<T>;

//namespace std
//{
//    template<>
//    class hash<Key>
//    {
//    public:
//        size_t operator() (const Key& key) const
//        {
//            size_t seed = 0;
//            auto i_hash = hash<int>()(key.i_th);
//            auto w_hash = hash<int>()(key.W);
//
//            seed ^= i_hash + 0x9e3779b9 + (seed << 6) + (seed >> 2);
//            seed ^= w_hash + 0x9e3779b9 + (seed << 6) + (seed >> 2);
//
//            return seed;
//        }
//    };
//}


void solve()
{
    using namespace std;
    int n;
    cin >> n;

    if (n < 1000)
        cout << "ABC" << endl;
    else
        cout << "ABD"<< endl;


}

int main()
{
    solve();
    return 0;
}