TypeError: '<' not supported between instances of 'str' and 'int'

[Svensation]

Dear all

I just tried my first steps with Python and found a - on the first sight - simple example in the internet. I tried to do it exactly the same way mentioned on the page. The programme looks as follows:

secret = 10
guess =0
i = 0

while guess != secret:
    guess = input("Raten Sie: ")
    if guess < secret:
        print ("Zu klein")
    if guess > secret:
        print ("Zu gross")
    i = i + 1
print ("Super, Sie haben es in "), i, ("Versuchen geschafft!")

Unfortunately it shows me the message: TypeError: '<' not supported between instances of 'str' and 'int'

What does that mean? What is wrong?

Thx for any help!