s=input()
t=input()
if 0<=len(s)-len(t)<=1:
	u=["."]*(len(s)+len(t))
	for i in range(len(s)):
		u[i*2]=s[i]
	for i in range(len(t)):
		u[i*2+1]=t[i]
	print("".join(u))
else:
	print("?")