a = input()
b = input()
if a[0] == '0' and len(a) > 1:
    print("NG")
elif b[0] == '0' and len(b) > 1:
    print("NG")
else:
    ok = True
    for c in a:
        if c < '0' or '9' < c:
            ok = False
    for c in b:
        if c < '0' or '9' < c:
            ok = False
    if ok:
        print("OK")
    else:
        print("NG")