a,b,c,d = input().strip().split()
n = 0
a = int(a)
b = int(b)
c = int(c)
d = int(d)
if a >= 90:
    n += 1
if b >= 90:
    n += 1
if c >= 90:
    n += 1
if d >= 90:
    n += 1
if n == 4:
    print("A")
elif n == 2 or n == 3:
    print("B")
elif n == 1 :
    print("C")
else:
    print("D")
/**************************************************************
	Problem: 1735
	User: lzk
	Language: Python
	Result: Accepted
	Time:82 ms
	Memory:34480 kb
****************************************************************/