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):
import math, sys
from bisect import bisect_left, bisect_right
from collections import Counter, defaultdict, deque
from copy import deepcopy
from functools import lru_cache
from heapq import heapify, heappop, heappush
from itertools import accumulate, combinations, permutations
input = sys.stdin.readline
mod = 10**9 + 7
ns = lambda: input().strip()
ni = lambda: int(input().strip())
nm = lambda: map(int, input().split())
nl = lambda: list(map(int, input().split()))

n = ni()

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

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

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

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 = input()

if len(N)<=3:
  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):
icase=0    
if icase==0:
    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('ABD')
else:
  print('ABC')

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

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

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

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

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

Solution (Python):
print(["ABC","ABD"][int(input())>=1000])

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

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

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

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

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

if '__main__' == __name__:
    resolve()

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

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

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

Solution (Python):
N = input()
if (int(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("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):
print("AB"+"CD"[int(input())>999])

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

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):
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 <= 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 < 1000 else "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):
n = int(input())
if n <= 999:
    print('ABC')
else:
    print('ABD')

Solution (Python):
import sys
def input(): return sys.stdin.readline().rstrip()

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

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

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

Solution (Python):
import sys, math
from itertools import permutations, combinations
from collections import defaultdict, Counter, deque
from math import factorial
from bisect import bisect_left 

sys.setrecursionlimit(10**7)
enu = enumerate
MOD = 10**9+7
def input(): return sys.stdin.readline()[:-1]
def pri(x): print('\n'.join(map(str, x)))

N = int(input())

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

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

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

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

if N < 1000:
  s = "ABC"
else:
  s = "ABD"

print(s)

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

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())
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 > 999:
    print("ABD")
else:
    print("ABC")

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

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

Solution (Python):
import itertools
def main():
  n = int(input())
  print("ABC"if n<=999 else "ABD")
if __name__ == '__main__':
  main()

Solution (Python):
print(["ABC","ABD"][len(input())==4])

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

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

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

Solution (Python):
import sys

n = int(sys.stdin.readline().rstrip())

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

if __name__ ==  '__main__':
    main()

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

Solution (Python):
import sys
import copy
import math
import bisect
import pprint
import bisect
from functools import reduce
from copy import deepcopy
from collections import deque

def lcm(x, y):
    return (x * y) // math.gcd(x, y)

if __name__ == '__main__':
    a = [int(i) for i in input().split()]

    if a[0] >999:
        print("ABD")
    else:
        print("ABC")

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

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

if 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):
print("AB"+("C"if int(input())<1000else"D"))

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

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

if n < 100:
    result = "ABC"
elif n > 999:
    n = n - 999
    result = "ABD" 
else:
    result = "ABC" 

print(result)

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):
def ABD(n):

    return "ABC" if n / 1000 < 1 else "ABD"

def main():
    n = int(input())
    print(ABD(n))

if __name__ == '__main__':
    main()

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

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

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

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

Solution (Python):
print('AB'+'DC'[int(input())<1000])

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

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())

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

Solution (Python):
import sys
import os

MOD = 10 ** 9 + 7


def main():
    if os.getenv("LOCAL"):
        sys.stdin = open("input.txt", "r")

    N = int(sys.stdin.buffer.readline().rstrip())
    print('ABC' if N <= 999 else 'ABD')


if __name__ == '__main__':
    main()

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

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

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

    print(ans)


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('ABD')
else:
  print('ABC')

Solution (Python):

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

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())

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

Solution (Python):

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

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

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

print(ans)

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

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

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

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

Solution (Python):

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

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

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

Solution (Python):


def main():
    import sys
    input = sys.stdin.readline
    sys.setrecursionlimit(10000000)
    from collections import Counter, deque
    
    from itertools import combinations, permutations, accumulate
    
    from bisect import bisect_left,bisect_right
    import heapq
    from math import floor, ceil
    

    
    

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

if __name__ == '__main__':
    main()

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

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

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


if __name__ == '__main__':
    main()

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

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

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

if N >= 1 and N <= 999:
  print("ABC")
else:
  print("ABD")

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

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

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

Solution (Python):









import sys



ipti = sys.stdin.readline
MOD = 10 ** 9 + 7
INF = float('INF')
sys.setrecursionlimit(10 ** 5)

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

if __name__ == '__main__':
    main()

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

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

a = 'ABC'
b = 'ABD'

if n >= 1000:
    print(b)
else:
    print(a)

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

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

Solution (Python):

n=int(input())
print('AB'+'CD'[n//1000])

Solution (Python):
print(["ABC","ABD"][len(input())>3])

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

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

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

Solution (Python):


n = int(input().strip())

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("ABC")
else:
  print("ABD")

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

Solution (Python):
n = int(input())
print('ABC' if 1 <= 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):
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):
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):
x = input()
if x < 1000:
    print "ABC"
if x > 999:
    print "ABD"

Solution (Python):
n=input()
if n<1000: 
  print "ABC" 
elif n < 1999:
  print "ABD"

Solution (Python):
N = input()
N = int(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):
import sys
 
stdin = sys.stdin
inf = 1 << 60
mod = 1000000007
 
ni = lambda: int(ns())
na = lambda: list(map(int, stdin.readline().split()))
nan = lambda x: [na() for _ in range(x)]
ns = lambda: stdin.readline().rstrip()
nsn = lambda x: [ns() for _ in range(x)]
nas = lambda: stdin.readline().split()

n = ni()

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

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

Solution (Python):
from heapq import heappush,heappop,heapify
from collections import deque,defaultdict,Counter
import itertools
from functools import *
from itertools import permutations,combinations,groupby
import sys
import bisect
import string
import math
import time
import random
def Golf():
    *a,=map(int,open(0))
def S_():
    return input()
def IS():
    return input().split()
def LS():
    return [i for i in input().split()]
def I():
    return int(input())
def MI():
    return map(int,input().split())
def LI():
    return [int(i) for i in input().split()]
def LI_():
    return [int(i)-1 for i in input().split()]
def NI(n):
    return [int(input()) for i in range(n)]
def NI_(n):
    return [int(input())-1 for i in range(n)]
def StoI():
    return [ord(i)-97 for i in input()]
def ItoS(nn):
    return chr(nn+97)
def LtoS(ls):
    return ''.join([chr(i+97) for i in ls])
def GI(V,E,Directed=False,index=0):
    org_inp=[]
    g=[[] for i in range(n)]
    for i in range(E):
        inp=LI()
        org_inp.append(inp)
        if index==0:
            inp[0]-=1
            inp[1]-=1
        if len(inp)==2:
            a,b=inp
            g[a].append(b)
            if not Directed:
                g[b].append(a)
        elif len(inp)==3:
            a,b,c=inp
            aa=(inp[0],inp[2])
            bb=(inp[1],inp[2])
            g[a].append(bb)
            if not Directed:
                g[b].append(aa)
    return g,org_inp
def GGI(h,w,search=None,replacement_of_found='.',mp_def={'

    mp=[1]*(w+2)
    found={}
    for i in range(h):
        s=input()
        for char in search:
            if char in s:
                found[char]=((i+1)*(w+2)+s.index(char)+1)
                mp_def[char]=mp_def[replacement_of_found]
        mp+=[1]+[mp_def[j] for j in s]+[1]
    mp+=[1]*(w+2)
    return h+2,w+2,mp,found
def bit_combination(k,n=2):
    rt=[]
    for tb in range(n**k):
        s=[tb//(n**bt)%n for bt in range(k)]
        rt+=[s]
    return rt
def show(*inp,end='\n'):
    if show_flg:
        print(*inp,end=end)
YN=['YES','NO']

mo=10**9+7
inf=float('inf')
l_alp=string.ascii_lowercase
u_alp=string.ascii_uppercase
ts=time.time()

input=lambda: sys.stdin.readline().rstrip()
 
def ran_input():
    import random
    n=random.randint(4,16)
    rmin,rmax=1,10
    a=[random.randint(rmin,rmax) for _ in range(n)]
    return n,a

show_flg=False
show_flg=True

ans=0

n=I()

if n<=999:
    ans='ABC'
else:
    ans='ABD'

print(ans)

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

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

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

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

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

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

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


if 1 <= N < 1000:
    print('ABC')
else:
    print('ABD')

Solution (Python):
n = int(input())
print("AB"+("C"*(n<=999) or "D"))

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

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

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

Solution (Python):
if int(input()) <= 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())
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('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())

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

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

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):
print(['ABC', 'ABD'][int(input())//1000])

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

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


if __name__ == '__main__':
    main()

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

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

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(_) for _ in input().split()][0]
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 <= 999:
    s = 'ABC'
else:
    s = 'ABD'

print(s)

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

Solution (Python):
usrInput = int(input())
isD = False

if usrInput >= 1000:
    isD = True
    number = usrInput - 999
else:
    isD = False
    number = usrInput

if isD:
    print("ABD")
else:
    print("ABC")

Solution (Python):
print("AB" + ("C" if int(input()) <= 999 else "D"))

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

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

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

Solution (Python):




def main():
    N = int(input())
    print('ABC'if N < 1000 else 'ABD')


if __name__ == "__main__":
    main()

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())
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("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("ABC")
else:
    print("ABD")

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

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

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

if number > 999:
  print("ABD")
else:
  print("ABC")

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

if number > 999:
  print("ABD")
else:
  print("ABC")

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

if number > 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 0 < n <= 999:
    print("ABC")
else:
    print("ABD")

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

Solution (Python):
print('AB'+'DC'[len(input())<4])

Solution (Python):
print('AB'+'CD'[(int(input())-1)//999])

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

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

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

Solution (Python):
print("AABBDC"[int(input())<1000::2])

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

Solution (Python):
import bisect
import cmath
import heapq
import itertools
import math
import operator
import os
import random
import re
import string
import sys
from collections import Counter, deque, defaultdict
from copy import deepcopy
from decimal import Decimal
from fractions import gcd
from functools import lru_cache, reduce
from operator import itemgetter, mul, add, xor

import numpy as np

if os.getenv("LOCAL"):
    sys.stdin = open("_in.txt", "r")

sys.setrecursionlimit(10 ** 9)
INF = float("inf")
IINF = 10 ** 18
MOD = 10 ** 9 + 7



n = int(sys.stdin.buffer.readline())
if n <= 999:
    print('ABC')
else:
    print('ABD')

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

Solution (Python):













a = max(map(int, input().split()))
if a <= 999:
    ans = 'ABC'
else:
    ans = "ABD"

print(ans)

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

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

Solution (Python):
"""
author : halo2halo
date : 24, Jan, 2020
"""

import sys



read = sys.stdin.buffer.read
readline = sys.stdin.buffer.readline
readlines = sys.stdin.buffer.readlines

a = int(readline())
print('ABC' if a < 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("ABD")
else:
  print("ABC")

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

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

Solution (Python):
print((["ABC"]+["ABD"])[int(input())//1000])

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):

from itertools import product, permutations, combinations

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

Solution (Python):
def main():
    from sys import stdin, setrecursionlimit
    setrecursionlimit(10**6)
    r = stdin.readline()[:-1]
    
    
    

    res = 0
    if len(r) == 4:
        print('ABD')
    else:
        print('ABC')

if __name__ == '__main__':
    main()