X = input()
Y = input()
if 0<=len(X)-len(Y)<=1:
    ans = ""
    turn = True
    x = 0
    y = 0
    while x+y<len(X)+len(Y):
        if turn:
            ans += X[x]
            x += 1
        else:
            ans += Y[y]
            y += 1
        turn = not turn
    print(ans)
else:
    print("?")