x=input()
y=input()
s=""
if len(x)==len(y)+1:
	for i in range(len(x)*2-1):
		if i%2==0:
			s+=x[i//2]
		else:
			s+=y[i//2]
	print(s)
elif len(x)==len(y):
	for i in range(len(x)*2):
		if i%2==0:
			s+=x[i//2]
		else:
			s+=y[i//2]
	print(s)
else:
	print("?")