# print_6067.py

a = int(input())

if (a < 0) and (a % 2 == 0):
    print("A")
if (a < 0) and (a % 2 != 0):
    print("B")
if (a > 0) and (a % 2 == 0):
    print("C")
if (a > 0) and (a % 2 != 0):
    print("D")
