import collections,sys,math,functools,operator,itertools,bisect,heapq,decimal,string,time,random
#input = sys.stdin.readline
#sys.setrecursionlimit(10**9)
#n = int(input())
#alist = list(map(int,input().split()))
#alist = []
s = input().rstrip()
t = input().rstrip()
#n,m = map(int,input().split())
#for i in range(n):
#    alist.append(list(map(int,input().split())))
if len(s) == len(t) or len(s) -1 == len(t):
    ans = []
    for i in range(len(t)):
        ans.append(s[i])
        ans.append(t[i])
    if len(s) -1 == len(t):
        ans.append(s[-1])
    print(''.join(ans))
else:
    print('?')