X = input()
Y = input()

S = ''
if len(X) == len(Y) or len(X) == len(Y) + 1:
    for i in range(min(len(X), len(Y))):
    	S += X[i]
    	S += Y[i]
    if len(X) > len(Y):
    	S += X[-1]
else:
	S = '?'

print(S)