x = input()
y = input()
l = len(x) - len(y)
if l == 0 or l == 1:
    for i in range(len(x+y)):
        if i % 2 == 0:
            print(x[i//2], end="")
        else:
            print(y[i//2], end="")
    print()
else:
    print("?")