#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(flag != 1 or ((int(bool0)!=0) and int(bool1)!=0)):
    print(get+get1)
else:
    print("NG")