How to use a string method on user input

[Exsul]

while input("Hit Enter or type \"stop.\" ") != "stop":

I'm trying to make it so that it doesn't matter if the user capitalizes "stop" or puts it in all caps. I've tried

while input("Hit Enter or type \"stop.\" ") != str.lower("stop"):

but that doesn't seem to do anything. I've also tried

while input(str.lower("Hit Enter or type \"stop.\" ")) != "stop":

but that just makes the prompt lower case. Help?