#coding:utf-8

flag = 0
try:
    get = input()
    get1 = input()
    bool1 = get1[0:1]
    bool0 = get[0:1]
    get = int(get)
    get1 = int(get1)
except:
    flag = 1

if((get == int(bool0) and get1 == int(bool1)) and flag == 0):
    print(get+get1)
elif((get == 0 or get1 == 0 and (flag == 0))):
    print(get+get1)
else:
    print("NG")