str_x = input()
str_y = input()

ligature = ""

if len(str_x) - len(str_y) == 0:
	for i in range(len(str_x)):
		ligature += (str_x[i] + str_y[i])
		
elif len(str_x) - len(str_y) == 1:
	str_y += " "
	for i in range(len(str_x)):
		ligature += (str_x[i] + str_y[i])
		
else:
	ligature = "?"
	
print(ligature)