X=input()
Y=input()
if len(X)-len(Y)==1:
    ans=[]
    for x,y in zip(X,Y):
        ans.append(x)
        ans.append(y)
    ans.append(X[-1])
    print("".join(ans))
elif len(X)-len(Y)==0:
    ans=[]
    for x,y in zip(X,Y):
        ans.append(x)
        ans.append(y)
    print("".join(ans))
else:
    print("?")