def f(s):
    if len(s) >= 2 and s[0] == "0":
        print("NG")
        exit()
def g(s):
    for c in s:
        if 0 <= ord(c) - ord("a") <= 25:
            print("NG")
            exit()
        if 0 <= ord(c) - ord("A") <= 25:
            print("NG")
            exit()
            
A = input()
B = input()
f(A)
f(B)
g(A)
g(B)
print("OK")