X = input()
Y = input()

if abs(len(X) - len(Y)) <= 1 and len(X) >= len(Y):
	result = ''
	for x, y in zip(X, Y):
		result += x
		result += y
	if len(X) > len(Y):
		result += X[-1]
	print(result)
else:
	print('?')