def Main():
    s=input()
    t=input()
    if len(s)<len(t) or len(s)>len(t)+1:
        print("?")
        return
    else:
        for i in range(len(s)+len(t)):
            if i%2==0:
                print(s[i//2],end="")
            else:
                print(t[i//2],end="")
    print()
Main()