X=input().strip()
Y=input().strip()

if len(X)-1<=len(Y)<=len(X):
    S=""
    while True:
        if X:
            S+=X[0]
            X=X[1:]
        else:
            break
        if Y:
            S+=Y[0]
            Y=Y[1:]
        else:
            break

    print(S)
else:
    print("?")