X = list(input())
Y = list(input())

ans = []
if len(X) == len(Y) or len(X) == len(Y) + 1:
    for i in range(len(X)):
        ans.append(X[i])
        if i < len(Y):
            ans.append(Y[i])
    print("".join(ans))
else:
    print("?")