# No.446 ゆきこーだーの雨と雪 (1)
a = input()
b = input()

isCorrect = 'OK'

for s in [a, b]:
    if len(s) > 1 and s[0] == '0':
        isCorrect = 'NG'
        break
    elif s.upper() != s.lower():
        isCorrect = 'NG'
        break
    elif s >= '12345':
        isCorrect = 'NG'
        break

print(isCorrect)