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 (Python):
N = int(input())
print("ABC" if N <1000 else "ABD")

Solution (Python):
N = int(input())

if N <= 999:
    print('ABC')

if N >= 1000 and N <= 1998:
    print('ABD')

Solution (Python):
n = int(input())
print('ABC' if n < 1000 else 'ABD')

Solution (Python):
def main(n: int) -> str:
    if n > 999:
        return 'ABD'
    else:
        return 'ABC'


if __name__ == "__main__":
    n = int(input())
    print(main(n))

Solution (Python):
n = int(input())

if n <= 999:
    print("ABC")
else:
    print("ABD")

Solution (Python):
D = int(input())

if D <= 999:
  print('ABC')
else:
  print('ABD')

Solution (Python):
N = int(input())
if N <1000:
  print('ABC')
else:
  print('ABD')

Solution (Python):
N=int(input())
if(N<1000):
    print("ABC")
else:
    print("ABD")

Solution (Python):
print("AB"+("C","D")[int(input())>999])

Solution (Python):
n = int(input())
print('ABC' if n <= 999 else 'ABD')

Solution (Python):
print('ABC' if int(input())<1000 else 'ABD')

Solution (Python):
print("ABD" if int(input())>999 else "ABC")

Solution (Python):
a = int(input())
print("ABC" if a <= 999 else "ABD")

Solution (Python):
N=int(input())
if N >999:
	print("ABD")
else: print("ABC")

Solution (Python):
n = int(input())
if n // 1000 >= 1:
    print('ABD')
else:
    print('ABC')

Solution (Python):
print("ABC" if int(input()) < 1000 else "ABD")

Solution (Python):
N = int(input())
if N >= 1000:
    print("ABD")
else:
    print("ABC")

Solution (Python):
N = int(input())
if N <= 999:
  print("ABC")
else:
  print("ABD")

Solution (Python):
n = int(input())
if 1 <= n <= 1998:
    if 1 <= n <= 999:
        print('ABC')
    else:
        print('ABD')
else:
    print('hoge!')

Solution (Python):
N = int(input())
if N <= 999:
    print('ABC')
elif N >= 1000 and N <= 1998:
    print('ABD')

Solution (Python):
num = int(input())
if num<=999:
  print("ABC")
else:
  print("ABD")

Solution (Python):
import sys
from collections import deque
from collections import  Counter
import statistics
import math
stdin = sys.stdin

ni = lambda: int(ns())
na = lambda: list(map(int, stdin.readline().split()))
ns = lambda: stdin.readline()

n = ni()
if n < 1000:
    print("ABC")
else:
    print("ABD")

Solution (Python):
n= int(input())
if n > 999:
    print('ABD')
else:
    print('ABC')

Solution (Python):
n=int(input())

if n>=1000:
 print('ABD')
else:
 print('ABC')

Solution (Python):
print("ABC") if int(input())<=999 else print("ABD")

Solution (Python):
N = int(input())
if N > 999:
    print('ABD')
else:
    print('ABC')

Solution (Python):
n = int(input())
print("ABC" if n<=999 else "ABD")

Solution (Python):
n=int(input())
print('ABC' if n<1000 else 'ABD')

Solution (Python):


n = int(input())

pref = ""
if n <= 999:
    pref = "ABC"
else:
    pref = "ABD"

print(pref)

Solution (Python):
n = int(input())
if 1 <= n <= 999:
    print('ABC')
else:
    print('ABD')

Solution (Python):
print("ABD"if int(input())//1000else"ABC")

Solution (Python):
N = int(input())
 
if N >= 1000:
  print("ABD")
else:
  print("ABC")

Solution (Python):
n=int(input())
if n>=1000:print("ABD")
else:print("ABC")

Solution (Python):
import sys
import math
from fractions import gcd





def lcm(a, b):
    return a * b // gcd(a, b)

def combination_count(n, r):
    return math.factorial(n) // (math.factorial(n - r) * math.factorial(r))

def permutations_count(n, r):
    return math.factorial(n) // math.factorial(n - r)

big_prime = 1000000007

"""


 =  sys.stdin.readline().rstrip()
 =  list(sys.stdin.readline().rstrip())


 =  int(sys.stdin.readline())
 =  map(int, sys.stdin.readline().split())
 =  list(map(int, sys.stdin.readline().split()))
 =  [list(map(int,list(sys.stdin.readline().split()))) for i in range(N)]
"""

N =  int(sys.stdin.readline())

if N <= 999:
    print("ABC")
else:
    print("ABD")

Solution (Python):


def main():

    print('ABC') if int(input()) <= 999 else print('ABD')



if __name__== "__main__":
    main()

Solution (Python):
n = int(input())

if n < 1000:
    print('ABC')
else:
    print('ABD')

Solution (Python):
n=int(input())

if n<=999:
  print('ABC')
else:
  print('ABD')

Solution (Python):
if int(input())<1000:
  print("ABC")
else:
  print("ABD")

Solution (Python):
print('ABC' if int(input()) < 1000 else 'ABD')

Solution (Python):
N=int(input())
if N>=1000:
    print("ABD")
else:
    print("ABC")

Solution (Python):
N = int(input())
print("ABC" if N<1000 else "ABD")

Solution (Python):
n=int(input())
if 1000>n:
    print("ABC")
else:
    print("ABD")

Solution (Python):

n = int(input())

if n <= 999:
    print('ABC')
else:

    print('ABD')

Solution (Python):
n =int(input())
print("ABC" if n<1000 else "ABD")

Solution (Python):
n = int(input())
print('ABC' if n <= 999 else 'ABD')

Solution (Python):
n = int(input())
if n >= 1000:
  print('ABD')
  
else:
  print('ABC')

Solution (Python):
print('ABC' if int(input())<1000 else 'ABD')

Solution (Python):
N=int(input())
print("ABC" if N < 1000 else "ABD")

Solution (Python):
if int(input())<1000:
  print("ABC")
else:
  print("ABD")

Solution (Python):
n=int(input())
if(n<1000):
    print("ABC")
else:
    print("ABD")

Solution (Python):
N = int(input())
if N >= 1000:
  print("ABD")
else:
  print("ABC")

Solution (Python):
print("ABD" if int(input())>999 else "ABC")

Solution (Python):
N = int(input())
if N <= 999:
    print("ABC")
else:
    print("ABD")

Solution (Python):
N = int(input())
if 1 <= N <= 999:
    print("ABC")
elif 1000 <= N <= 1998:
    print("ABD")

Solution (Python):
N = int(input())
if N<1000:
  print("ABC")
else:
  print("ABD")

Solution (Python):
def main():
    N = int(input())
    if N < 1000:
        return "ABC"
    else:
        return "ABD"

if __name__ == '__main__':
    print(main())

Solution (Python):
n = int(input())
if n > 999:
    print("ABD")
else:
    print("ABC")

Solution (Python):
print("ABC" if int(input()) < 1000 else "ABD")

Solution (Python):
a = int(input())
print('ABC' if a<=999 else 'ABD')

Solution (Python):
print("ABD" if int(input())>999 else "ABC")

Solution (Python):
N = int(input())
print('ABC' if N <= 999 else 'ABD')

Solution (Python):
print('ABC' if int(input())<1000 else 'ABD')

Solution (Python):
print('ABC' if int(input()) < 1000 else 'ABD')

Solution (Python):
print("ABC" if int(input()) < 1000 else "ABD")

Solution (Python):
n = int(input())
print("ABC" if n < 1000 else "ABD")

Solution (Python):
n = int(input())
if 1 <= n <= 999:
  print("ABC")
else:
  print("ABD")

Solution (Python):
N = int(input())
print('ABC' if N<1000 else 'ABD')

Solution (Python):
N = int(input())
if N >= 1000:
    print("ABD")
else:
    print("ABC")

Solution (Python):
N=int(input())
a='ABD'
b='ABC'

if N<=999:
  print(b)
else:
  print(a)

Solution (Python):
n = int(input())
if n < 1000:
    print("ABC")
else:
    print("ABD")

Solution (Python):
def resolve():
    n = int(input())
    print("ABC") if n < 1000 else print("ABD")

if __name__ == "__main__":
    resolve()

Solution (Python):
print("ABC" if int(input()) < 1000 else "ABD")

Solution (Python):
N=input()
N=int(N)

if N<=999:
    print("ABC")
else:
    print("ABD")

Solution (Python):
print('AABBCD'[int(input())>=1000::2])

Solution (Python):
n=int(input())

if n<1000:
	print('ABC')
else:
	print('ABD')

Solution (Python):
N = int(input())

if N < 1000:
  print("ABC")
else:
  print("ABD")

Solution (Python):
N = int(input())

if N <= 999:
  print("ABC")
else:
  print("ABD")

Solution (Python):
n=int(input())
if n>999:
  print("ABD")
else:
  print("ABC")

Solution (Python):
print('ABC' if int(input()) <= 999 else 'ABD')

Solution (Python):
n=int(input())
if n<1000:
    print('ABC')
else:
    print('ABD')

Solution (Python):
import sys
def input(): return sys.stdin.readline().strip()
n=int(input())
print('AB' + ('C' if n < 1000 else 'D'))

Solution (Python):
a = int(input())

print('ABC' if a < 1000 else 'ABD')

Solution (Python):
print("ABC" if int(input())<=999 else "ABD")

Solution (Python):
n = int(input())
print("ABC" if n <= 999 else "ABD")

Solution (Python):
n = int(input())
print('ABC' if n <= 999 else 'ABD')

Solution (Python):
N=int(input())

if N<=999:
    print('ABC')
else :
    print('ABD')

Solution (Python):
def test():
    x = int(input())
    if x < 1000:
        print("ABC")
    else:
        print("ABD")


if __name__ == "__main__":
    test()

Solution (Python):
def main():
    N = int(input())

    if N <= 999:
        print('ABC')
    else:
        print('ABD')

main()

Solution (Python):
a = int(input())

if a > 999:
    print('ABD')
else:
    print('ABC')

Solution (Python):
n=int(input())
print("ABC" if n<1000 else "ABD")

Solution (Python):
if int(input()) < 1000:
  print("ABC")
else:
  print("ABD")

Solution (Python):
n = int(input())
print("ABC" if n <= 999 else "ABD")

Solution (Python):
print("ABC" if int(input())<1000 else "ABD")

Solution (Python):
print('AABBCD'[int(input())>999::2])

Solution (Python):
n = int(input())
print("ABC" if n >= 1 and n <= 999 else "ABD")

Solution (Python):
N = int(input())
print("ABC" if N < 1000 else "ABD")

Solution (Python):
N = int(input())

ans = "ABD"
if (N >= 1 and N < 1000):
  ans = "ABC"
print(ans)

Solution (Python):
if (int(input()) < 1000):
  print("ABC")
else:
  print("ABD")

Solution (Python):
N = int(input())
print ("ABC" if N <= 999 else "ABD")

Solution (Python):
N = int(input())

if N >= 1000:
    print('ABD')
else:
    print('ABC')

Solution (Python):
N = int(input())
if N >= 1000:
  print("ABD")
else:
  print("ABC")

Solution (Python):
print('AB'+['D','C'][len(input())<4])

Solution (Python):
print(['ABD','ABC'][len(input())<4])

Solution (Python):
N=int(input())
print("ABC" if N<1000 else "ABD")

Solution (Python):

n = int(input())
print('ABC' if n <= 999 else 'ABD')

Solution (Python):
n = int(input())
print('ABC' if n <= 999 else 'ABD')

Solution (Python):
n = int(input())

if n<=999:
  print('ABC')

else:
  print('ABD')

Solution (Python):
N = int(input())
if N < 1000:
  print("ABC")
else:
  print("ABD")

Solution (Python):
x = int(input())

if x < 1000:
  print("ABC")
else:
  print("ABD")

Solution (Python):
n=int(input())
if n>999:
    print('ABD')
else:
    print('ABC')

Solution (Python):
N = int(input())
if N<=999:
	print("ABC")
else:
	print("ABD")

Solution (Python):
n = int(input())

if n < 1000:
  print("ABC")
else:
  print('ABD')

Solution (Python):
n = int(input())
if n <= 999:
    print('ABC')
else:
    print('ABD')

Solution (Python):
N=int(input())
if N<=999:
    print("ABC")
else:
    print("ABD")

Solution (Python):
print('ABC' if int(input())<=999 else 'ABD')

Solution (Python):
N = int(input())

if N <= 999:
  print("ABC")
else:
  print("ABD")

Solution (Python):

n = int(input())
if n < 1000:
  print('ABC')
else:
  print('ABD')

Solution (Python):


N = int(input())

if N <= 999:
    print("ABC")
else:
    print("ABD")

Solution (Python):
from sys import stdin
N = int(stdin.readline().rstrip())
if N <= 999:
    print("ABC")
    
else:
    print("ABD")

Solution (Python):
a = int(input())
if 1 <= a <= 999:
    print("ABC")
else:
    print("ABD")

Solution (Python):
n = int(input())
if n > 999:
  print("ABD")
else:
  print("ABC")

Solution (Python):
N = int(input())

if N >= 1000:
    print('ABD')
else:
    print('ABC')

Solution (Python):
if int(input()) <= 999:
    print("ABC")
else:
    print("ABD")

Solution (Python):
n = int(input())
if n < 1000:
    print("ABC")
else:
    print("ABD")

Solution (Python):
N = int(input())

if N <= 999:
    print("ABC")
else:
    print("ABD")

Solution (Python):
N = int(input())
if N<=999:
    print('ABC')
else:
    print('ABD')

Solution (Python):
n = int(input())
if n > 999:
    print("ABD")
else:
    print("ABC")

Solution (Python):
N = int(input())
if N < 1000:
    print('ABC')
else:
    print('ABD')

Solution (Python):
n=int(input())
print("ABC" if n<=999 else "ABD")

Solution (Python):
N = int(input())
if N <=999:
  print("ABC")
else:
  print("ABD")

Solution (Python):
n=int(input())
print('ABC' if n<1000 else 'ABD')

Solution (Python):
print("ABC" if int(input()) < 1000 else "ABD")

Solution (Python):
N = int(input())

if N >= 1000:
    print('ABD')
else:
    print('ABC')

Solution (Python):
n = int(input())
if n<1000:
    print("ABC")
else:
    print("ABD")

Solution (Python):
print("AB"+"CD"[len(input())>3])

Solution (Python):
N=int(input())
if N<1000:
  print("ABC")
else:
  print("ABD")

Solution (Python):
N = int(input())
if N < 1000:
    print("ABC")
else:
    print("ABD")

Solution (Python):
n = int(input())
if 1 <= n <= 999:
  print('ABC')
else:
  print('ABD')

Solution (Python):
n = int(input())
if n <= 999:
  print("ABC")
else:
  print("ABD")

Solution (Python):
x = int(input())
if x < 1000:
  print('ABC')
else:
  print('ABD')

Solution (Python):
a=int(input())
if a>=1000:
    print("ABD")
else:
    print("ABC")

Solution (Python):
n = int(input())
print('ABC' if n<=999 else 'ABD')

Solution (Python):
print('ABC' if int(input())<1000 else 'ABD')

Solution (Python):
print('ABC' if int(input()) <= 999 else 'ABD')

Solution (Python):
n = int(input())
if n >= 1000:
  print('ABD')
else:
  print('ABC')

Solution (Python):
N = int(input())

if N < 1000:
    print('ABC')
else:
    print('ABD')

Solution (Python):

n = int(input())

print("ABC" if n <= 999 else "ABD")

Solution (Python):
n = int(input())
if n >= 1000:
    print("ABD")
else:
    print("ABC")

Solution (Python):


a = int(input())

if a <= 999:
    print("ABC")
else:
    print("ABD")

Solution (Python):
print("ABC" if int(input())<1000 else "ABD")

Solution (Python):
N = int(input())
print(("ABC" if N < 1000 else "ABD"))

Solution (Python):
n = int(input())
if n < 1000:
  print('ABC')
else:
  print('ABD')

Solution (Python):
n = int(input())
if n < 1000:
  print("ABC")
else:
  print("ABD")

Solution (Python):
n=int(input())
if n <= 999:
    print('ABC')
else:
    print('ABD')

Solution (Python):
if int(input())<1000:
  print("ABC")
else:
  print("ABD")

Solution (Python):
N = int(input())
if N >999:
  print('ABD')
else:
  print('ABC')

Solution (Python):
def main():
    N = int(input())
    if N >= 1000:
        print("ABD")
    else:
        print("ABC")


if __name__ == "__main__":
    main()

Solution (Python):
N = int(input())
if N <= 999:
    print("ABC")
else:
    print("ABD")

Solution (Python):
N = int(input())
if N >= 1000:
  print('ABD')
else:
  print('ABC')

Solution (Python):
n=int(input())
if n >= 1000:print("ABD")
else:print("ABC")

Solution (Python):
a = int(input())
if a<= 999:
  print('ABC')
else:
  print('ABD')

Solution (Python):
if 1<= int(input()) <= 999:
    print("ABC")
else:
    print("ABD")

Solution (Python):
n=int(input())
print('ABC' if n<1000 else 'ABD')

Solution (Python):
n = int(input())
if n < 1000:
    print('ABC')
else:
    print('ABD')

Solution (Python):
import sys, re, os
from collections import deque, defaultdict, Counter
from math import ceil, sqrt, hypot, factorial, pi, sin, cos, radians
from itertools import permutations, combinations, product, accumulate
from operator import itemgetter, mul
from copy import deepcopy
from string import ascii_lowercase, ascii_uppercase, digits
from fractions import gcd
 
def input(): return sys.stdin.readline().strip()
def INT(): return int(input())
def MAP(): return map(int, input().split())
def LIST(): return list(map(int, input().split()))
sys.setrecursionlimit(10 ** 9)
INF = float('inf')
mod = 10 ** 9 + 7

N = INT()

if N < 1000:
    print("ABC")
else:
    print("ABD")

Solution (Python):
a = int(input())
if a // 1000 == 1:
    print("ABD")
else:
    print("ABC")

Solution (Python):

N = int(input())
if N <= 999:
    print("ABC")
else:
    print("ABD")

Solution (Python):
print('AB'+'CD'[int(input())>999])

Solution (Python):

from collections import defaultdict
from collections import deque
from heapq import heappush, heappop
import sys
import math
import bisect
import random
import itertools
sys.setrecursionlimit(10**5)
stdin = sys.stdin
def LI(): return list(map(int, stdin.readline().split()))
def LF(): return list(map(float, stdin.readline().split()))
def LI_(): return list(map(lambda x: int(x)-1, stdin.readline().split()))
def II(): return int(stdin.readline())
def IF(): return float(stdin.readline())
def LS(): return list(map(list, stdin.readline().split()))
def S(): return list(stdin.readline().rstrip())
def IR(n): return [II() for _ in range(n)]
def LIR(n): return [LI() for _ in range(n)]
def FR(n): return [IF() for _ in range(n)]
def LFR(n): return [LI() for _ in range(n)]
def LIR_(n): return [LI_() for _ in range(n)]
def SR(n): return [S() for _ in range(n)]
def LSR(n): return [LS() for _ in range(n)]
mod = 1000000007
inf = float("INF")


def A():
    n = II()
    if n < 1000:
        print("ABC")
    else:
        print("ABD")
    return


def B():
    return


def C():
    n = II()
    dp = [inf for i in range(n + 1)]
    ans = [1]
    x = 6
    while x <= n:
        ans.append(x)
        x = x * 6
    x = 9
    while x <= n:
        ans.append(x)
        x = x * 9
    ans.sort()
    for i in ans:
        dp[i] = 1
    for i in range(1, n + 1):
        if not i in ans:
            a = bisect.bisect_left(ans, i)
            for k in range(a):
                
                dp[i] = min(dp[i - ans[k]] + 1, dp[i])
    print(dp[n])

    return


def D():
    n, c = LI()
    D = LIR(c)
    C = LIR_(n)
    CL = list(itertools.permutations(range(c), 3))
    ans = inf
    amari0 = [0 for i in range(30)]
    amari1 = amari0[::1]
    amari2 = amari0[::1]
    for y in range(n):
        for x in range(n):
            amari = (x + y) % 3
            if amari == 0:
                amari0[C[y][x]] += 1
            if amari == 1:
                amari1[C[y][x]] += 1
            if amari == 2:
                amari2[C[y][x]] += 1
    for c0, c1, c2 in CL:
        ansb = 0
        for i in range(c):
            ansb += D[i][c0] * amari0[i]
            ansb += D[i][c1] * amari1[i]
            ansb += D[i][c2] * amari2[i]
        ans = min(ans, ansb)

            
    print(ans)

    return


def E():
    return


def F():
    return


def G():
    return


def H():
    return


if __name__ == '__main__':
    A()

Solution (Python):
print('AB'+chr(67+int(input())//1000))

Solution (Python):
N = int(input())



if N < 1000:
    print('ABC')
else:
    print('ABD')

Solution (Python):
n = int(input())
print('ABC') if n < 1000 else print('ABD')

Solution (Python):
n = int(input())
print('ABC' if n < 1000 else 'ABD')

Solution (Python):
print('ABD') if int(input()) > 999 else print('ABC')

Solution (Python):
from functools import reduce
import math

def main():
    
    
    
    

    
    
    
    
    
    

    
    

    
    
    
    
    
    
    
    
    
    INF = float("inf")

    
    MOD = 10**9+7
    
    
    
    
    
    
    
    
    
    
    
    
    
    
    

    
    
    
    
    N = int(input())
    if N>999:
        print('ABD')
    else:
        print('ABC')
        
if __name__ == '__main__':
    main()

Solution (Python):
n = int(input())
if n <= 999:
    print("ABC")
else:
    print("ABD")

Solution (Python):
a = int(input())
if a >= 1000:
    print("ABD")
else:
    print("ABC")

Solution (Python):
N = int(input())
if N <= 999: print('ABC')
else: print('ABD')

Solution (Python):
N = int(input())
if N < 1000:
    print("ABC")
else:
    print("ABD")

Solution (Python):
import sys

def input():
    return sys.stdin.readline().rstrip()

if __name__ == "__main__":
    n = int(input())

    print("ABC" if n <= 999 else "ABD")

Solution (Python):
a=int(input())
print("ABC" if a<1000 else "ABD")

Solution (Python):
n = int(input())
 
if n > 999:
    print('ABD')
else:
    print('ABC')

Solution (Python):
n = int(input())

if n < 1000:
    print("ABC")
else:
    print("ABD")

Solution (Python):
n = int(input())

if n >= 1000:
    print("ABD")
else:
    print("ABC")

Solution (Python):

N = int(input())

if N <= 999:
    print('ABC')
else:
    print('ABD')

Solution (Python):
n=int(input())
if n >= 1000:print("ABD")
else:print("ABC")

Solution (Python):
N = int(input())
if N >= 1000:
    print("ABD")
else:
    print("ABC")

Solution (Python):


r = int(input())


if r < 1000:
  print("ABC")
else:
  print("ABD")

Solution (Python):
N = int(input())

if N > 999:
  print('ABD')
else:
  print('ABC')

Solution (Python):
n=int(input())
if n<1000:
  print("ABC")
else:
  print("ABD")

Solution (Python):
print('AB%s'%chr(67+(len(input())>3)))

Solution (Python):
print("ABC") if int(input())<=999 else print("ABD")

Solution (Python):
if int(input()) <= 999:
  print("ABC")
else:
  print("ABD")

Solution (Python):
a = int(input())
if a <= 999:
  print("ABC")
else:
  print("ABD")

Solution (Python):
a=int(input())
if a<1000:
  print("ABC")
else:
  print("ABD")

Solution (Python):
a=int(input())
if a<1000:
  print("ABC")
else:
  print("ABD")

Solution (Python):
n = int(input())
if n<1000:
    print('ABC')
else:
    print('ABD')

Solution (Python):



N = int(input())


ans = 'ABC' if N < 1000 else 'ABD'


print(ans)

Solution (Python):
N = int(input())

if N >= 1000:
  print('ABD')
else:
  print('ABC')

Solution (Python):

import sys
import copy
import collections
from bisect import bisect_left
from bisect import bisect_right
from collections import defaultdict
from heapq import heappop, heappush
import numpy as np
import statistics
from statistics import mean, median,variance,stdev
import math

def main():
	N = int(input())
	
	if N <= 999:
		print("ABC")
	else:
		print("ABD")
	
	
if __name__ == "__main__":
	main()

Solution (Python):
print("ABD" if int(input()) >= 1000 else "ABC")

Solution (Python):
N = int(input())
if N <= 999:
  print("ABC")
else:
  print("ABD")

Solution (Python):

answer = int(input())
if answer >= 1000:
    print("ABD")
else:
    print("ABC")

Solution (Python):

N = int(input())
if N//1000==0:
    print("ABC")
else:
    print("ABD")

Solution (Python):
print("ABC" if int(input())<1000 else "ABD")

Solution (Python):
n = int(input())

if n <= 999:
    print("ABC")
else:
    print("ABD")

Solution (Python):
N = int(input())
if N <1000:
    print("ABC")
else:
    print("ABD")

Solution (Python):
nl = lambda: list(map(int, input().split()))
sl = lambda: input().split()
n = lambda: int(input())
s = lambda: input()

N = n()

if N <= 999:
    print('ABC')
else:
    print('ABD')

Solution (Python):
N = int(input())
if N<1000:
    print("ABC")
else:
    print("ABD")

Solution (Python):
N = int(input())

if N <= 999:
  print("ABC")
else:
  print("ABD")

Solution (Python):
N = int(input())

if N <= 999:
    print ("ABC")

else:
    print ("ABD")

Solution (Python):
n = int(input())
if n < 1000:
    print('ABC')
else:
    print('ABD')

Solution (Python):
N=int(input())

if N < 1000:
  print("ABC")
else:
  print("ABD")

Solution (Python):
N = int(input())
if N < 1000:
    print('ABC')
else:
    print('ABD')

Solution (Python):
n = int(input())
if n < 1000:
  print('ABC')
else:
  print('ABD')

Solution (Python):
n=int(input())
print('ABC' if n<1000 else 'ABD')

Solution (Python):
n = int(input())
print('ABC' if n < 1000 else 'ABD')

Solution (Python):
n = int(input())
if n <= 999:
    print("ABC")
else:
    print("ABD")

Solution (Python):
n = int(input())
title = ""
if n > 999:
  title = "ABD"
else:
  title = "ABC"
print(title)

Solution (Python):
n = int(input())
if n < 1000:
    print("ABC")
else:
    print("ABD")

Solution (Python):
N = int(input())
S = 'ABD' if N >= 1000 else 'ABC'
print(S)

Solution (Python):
input_line = int(input())

if input_line <= 999:
  print("ABC")
elif input_line <= 1998:
  print("ABD")

Solution (Python):
N = int(input())

if 1 <= N <= 999:
    print('ABC')
else:
    print('ABD')

Solution (Python):
n = int(input())
if n >= 1000:
    print("ABD")
else:
    print("ABC")

Solution (Python):
n = int(input())
if n < 1000:
        print("ABC")
else:
        print("ABD")

Solution (Python):
print('ABC' if int(input()) <= 999 else 'ABD')

Solution (Python):
N = int(input())
if N >= 1000:
  print("ABD")
else:
  print("ABC")

Solution (Python):
n = int(input())
if n < 1000:
  print('ABC')
else:
  print('ABD')

Solution (Python):
N = int(input())
print("ABC" if N < 1000 else "ABD")

Solution (Python):
x=int(input())
if x<1000:
  print("ABC")
else:print("ABD")

Solution (Python):
if int(input())>999:
  print('ABD')
else:
  print('ABC')

Solution (Python):
n=int(input())
a='ABC' if n<1000 else 'ABD'
print(a)

Solution (Python):
N = int(input())
if N < 1000:
    print('ABC')
else:
    print('ABD')

Solution (Python):
N = int(input())
if N >= 1000:
    print("ABD")
else:
    print("ABC")

Solution (Python):
n = int(input())

if n < 1000:
  print('ABC')
else:
  print('ABD')

Solution (Python):
s = input()
print('ABC') if len(s)<4 else print('ABD')

Solution (Python):
print("ABC" if int(input())<1000 else "ABD")

Solution (Python):
print('ABC' if int(input()) < 1000 else 'ABD')

Solution (Python):
print('ABC' if int(input()) < 1000 else 'ABD')

Solution (Python):
N = int(input())
if N <= 999:
  print("ABC")
else:
  print("ABD")

Solution (Python):
N = int(input())
offset = 'ABC' if N <= 999 else 'ABD'
print(offset)

Solution (Python):
N = int(input())
print('ABD' if N >= 1000 else 'ABC')

Solution (Python):
N = int(input())
if N <= 999:
  print("ABC")
else:
  print("ABD")

Solution (Python):
N = int(input())
if N>=1 and N<1000:
    print('ABC')
else:
    print('ABD')

Solution (Python):
n = int(input())

if n <= 999 and n >= 1:
    print('ABC')

else :
    print('ABD')

Solution (Python):
def abc():
    n = int(input().rstrip())
    print('ABC' if n <= 999 else 'ABD')


abc()

Solution (Python):
n = int(input())
if n > 999:
  print("ABD")
else:
  print("ABC")

Solution (Python):
N = int(input())

if N < 1000:
    print('ABC')
else:
    print('ABD')

Solution (Python):
n=int(input())
if n<1000:
    print('ABC')
else:
    print('ABD')

Solution (Python):
if __name__ == '__main__':
    N = int(input())

    if N <= 999:
        print("ABC")
    else:
        print("ABD")

Solution (Python):
if int(input()) > 999:
    print("ABD")
else:
    print("ABC")

Solution (Python):
N = input()
if 999 < int(N):
    print('ABD')
else:
    print('ABC')

Solution (Python):
N = int(input())
if N <= 999:
    print('ABC')
else:
    print('ABD')

Solution (Python):
N = int(input())

if N < 1000:
  print("ABC")
else:
  print("ABD")

Solution (Python):
N = int(input())

if N < 1000:
  print("ABC")
else:
  print("ABD")

Solution (Python):
N = int(input())
if N >= 1000:
    print('ABD')
else:
    print('ABC')

Solution (Python):
n = int(input())
if n < 1000:
  print("ABC")
else:
  print("ABD")

Solution (Python):
n = int(input())
if n < 1000 :
        print('ABC')
else :
        print('ABD')

Solution (Python):
n = int(input())
if n <= 999:
    print('ABC')
else:
    print('ABD')

Solution (Python):
print('ABC' if int(input())<=999 else 'ABD')

Solution (Python):
N = int(input())

if(N <= 999):
    print('ABC')
else:
    print('ABD')

Solution (Python):
n = int(input())
print("ABC" if n<1000 else "ABD")

Solution (Python):
n = int(input())
print("ABC" if n<1000 else "ABD")

Solution (Python):
N = int(input())
if N <= 999:
    print("ABC")
elif 1000 <= N <= 1998:
    print("ABD")

Solution (Python):
print("AABBCD"[int(input())>999::2])

Solution (Python):
n = int(input())
if n < 1000:
    print("ABC")
else:
    print("ABD")

Solution (Python):
n = int(input())
if n < 1000:
    print("ABC")
else:
    print("ABD")

Solution (Python):
a=int(input())
if a<=999:
  print("ABC")
else:
  print("ABD")

Solution (Python):
n = int(input())
if n<=999:
    print("ABC")
else:
    print("ABD")

Solution (Python):
n=int(input())
if n<=999:
    print('ABC')
else:
    print('ABD')

Solution (Python):
n=int(input())
print("ABC" if n<1000 else "ABD")

Solution (Python):


n = int(input())

if n < 1000:
    print('ABC')
else:
    print('ABD')

Solution (Python):
n = int(input())
if n < 1000:
  print("ABC")
else:
  print("ABD")

Solution (Python):
n = int(input())

flg = "ABC"

if n >= 1000:
    flg = "ABD"
print(flg)

Solution (Python):
n = int(input())

if n <=999:
    print("ABC")
else:
    print("ABD")

Solution (Python):
N = int(input())
print("ABC" if N < 1000 else "ABD")

Solution (Python):
n=int(input())
print("ABC" if n<1000 else"ABD")

Solution (Python):
n = int(input())
ans = None
if n < 1000:
    ans = 'ABC'
else:
    ans = 'ABD'
print(ans)

Solution (Python):
num = int(input())
if num<=999:
    print("ABC")
else:
    print("ABD")

Solution (Python):
n=int(input())
if n<1000:
  print("ABC")
else:
  print("ABD")

Solution (Python):
n=int(input())

if n<=999:
    print("ABC")

else:
    print("ABD")

Solution (Python):
contest = ['ABC', 'ABD']
N = int(raw_input())
print contest[(N-1)/999]

Solution (Python):
if len(input()) == 4:
  print("ABD")
else:
  print("ABC")

Solution (Python):
print("ABC" if int(input()) <= 999 else "ABD")

Solution (Python):

import sys


def solve(N: int):
    if N <= 999:
        print("ABC")
    else:
        print("ABD")



def main():
    def iterate_tokens():
        for line in sys.stdin:
            for word in line.split():
                yield word
    tokens = iterate_tokens()
    N = int(next(tokens))  
    solve(N)

if __name__ == '__main__':
    main()

Solution (Python):
N = int(input())
if N <= 999:
  print('ABC')
else:
  print('ABD')

Solution (Python):
n = int(input())
if n <= 999:
    print('ABC')
else:
    print('ABD')

Solution (Python):
n = int(input())
if n < 1000:
  print('ABC')
else:
  print('ABD')

Solution (Python):
n=int(input())
print("ABC" if n<=999 else "ABD")

Solution (Python):
if int(input()) >= 1000:
  print("ABD")
else:
  print("ABC")

Solution (Python):
n = int(input())

if n >= 1000:
    print("ABD")
else:
    print("ABC")

Solution (Python):
a = int(input())

if (a < 1000) :
    print("ABC")
else :
    print("ABD")

Solution (Python):
n = int(input())
if 1000 <= n:
    print("ABD")
else:
    print("ABC")

Solution (Python):
print("ABC" if int(input()) < 1000 else "ABD")

Solution (Python):
n=int(input())
if n<1000:
  print("ABC")
else:
  print("ABD")

Solution (Python):
n = int(input())
print("ABD" if n > 999 else "ABC")

Solution (Python):
N = int(input())
if N <= 999:
    print("ABC")
else:
    print("ABD")

Solution (Python):
N = int(input())
if N <= 999:
    print("ABC")
else:
    print("ABD")

Solution (Python):
N = int(input())
if N < 1000:
    print("ABC")
else:
    print("ABD")

Solution (Python):
n = int(input())
if n <= 999:
  print('ABC')
else:
  print('ABD')