a = input()
b = input()

for i in a:
    if i.isdigit() != True:
        print('NG')
        exit()

for i in b:
    if i.isdigit() != True:
        print('NG')
        exit()

A = str(int(a))
B = str(int(b))

if len(a) != len(A):
    print('NG')
    exit()

if len(b) != len(B):
    print('NG')
    exit()

print('OK')